diff --git a/src/Model/Contact.php b/src/Model/Contact.php
index 4a10fd98ea..c20435278f 100644
--- a/src/Model/Contact.php
+++ b/src/Model/Contact.php
@@ -1395,9 +1395,17 @@ class Contact
 		}
 
 		if ($data['network'] == Protocol::DIASPORA) {
-			DI::dsprContact()->updateFromProbeArray($data);
+			try {
+				DI::dsprContact()->updateFromProbeArray($data);
+			} catch (\InvalidArgumentException $e) {
+				Logger::error($e->getMessage(), ['url' => $url, 'data' => $data]);
+			}
 		} elseif (!empty($data['networks'][Protocol::DIASPORA])) {
-			DI::dsprContact()->updateFromProbeArray($data['networks'][Protocol::DIASPORA]);
+			try {
+				DI::dsprContact()->updateFromProbeArray($data['networks'][Protocol::DIASPORA]);
+			} catch (\InvalidArgumentException $e) {
+				Logger::error($e->getMessage(), ['url' => $url, 'data' => $data['networks'][Protocol::DIASPORA]]);
+			}
 		}
 
 		self::updateFromProbeArray($contact_id, $data);
@@ -2485,15 +2493,23 @@ class Contact
 			return false;
 		}
 
-		$ret = Probe::uri($contact['url'], $network, $contact['uid']);
+		$data = Probe::uri($contact['url'], $network, $contact['uid']);
 
-		if ($ret['network'] == Protocol::DIASPORA) {
-			DI::dsprContact()->updateFromProbeArray($ret);
-		} elseif (!empty($ret['networks'][Protocol::DIASPORA])) {
-			DI::dsprContact()->updateFromProbeArray($ret['networks'][Protocol::DIASPORA]);
+		if ($data['network'] == Protocol::DIASPORA) {
+			try {
+				DI::dsprContact()->updateFromProbeArray($data);
+			} catch (\InvalidArgumentException $e) {
+				Logger::error($e->getMessage(), ['id' => $id, 'network' => $network, 'contact' => $contact, 'data' => $data]);
+			}
+		} elseif (!empty($data['networks'][Protocol::DIASPORA])) {
+			try {
+				DI::dsprContact()->updateFromProbeArray($data['networks'][Protocol::DIASPORA]);
+			} catch (\InvalidArgumentException $e) {
+				Logger::error($e->getMessage(), ['id' => $id, 'network' => $network, 'contact' => $contact, 'data' => $data]);
+			}
 		}
 
-		return self::updateFromProbeArray($id, $ret);
+		return self::updateFromProbeArray($id, $data);
 	}
 
 	/**
@@ -3193,8 +3209,9 @@ class Contact
 		self::clearFollowerFollowingEndpointCache($contact['uid']);
 
 		$cdata = self::getPublicAndUserContactID($contact['id'], $contact['uid']);
-
-		DI::notification()->deleteForUserByVerb($contact['uid'], Activity::FOLLOW, ['actor-id' => $cdata['public']]);
+		if (!empty($cdata['public'])) {
+			DI::notification()->deleteForUserByVerb($contact['uid'], Activity::FOLLOW, ['actor-id' => $cdata['public']]);
+		}
 	}
 
 	/**
diff --git a/src/Module/DFRN/Notify.php b/src/Module/DFRN/Notify.php
index 34cf21f11d..14b121e810 100644
--- a/src/Module/DFRN/Notify.php
+++ b/src/Module/DFRN/Notify.php
@@ -70,18 +70,8 @@ class Notify extends BaseModule
 				throw new \Friendica\Network\HTTPException\InternalServerErrorException();
 			}
 			$this->dispatchPrivate($user, $postdata);
-		} elseif (!$this->dispatchPublic($postdata)) {
-			(new Salmon(
-				$this->database,
-				$this->l10n,
-				$this->baseUrl,
-				$this->args,
-				$this->logger,
-				$this->profiler,
-				$this->response,
-				$this->server,
-				$this->parameters
-			))->rawContent($request);
+		} else {
+			$this->dispatchPublic($postdata);
 		}
 	}
 
diff --git a/src/Module/Notifications/Ping.php b/src/Module/Notifications/Ping.php
index 76cdd9f770..df75c047af 100644
--- a/src/Module/Notifications/Ping.php
+++ b/src/Module/Notifications/Ping.php
@@ -48,6 +48,7 @@ use Friendica\Navigation\Notifications\Factory;
 use Friendica\Navigation\Notifications\Repository;
 use Friendica\Navigation\Notifications\ValueObject;
 use Friendica\Navigation\SystemMessages;
+use Friendica\Network\HTTPException;
 use Friendica\Protocol\Activity;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Profiler;
@@ -229,7 +230,11 @@ class Ping extends BaseModule
 
 			// merge all notification types in one array
 			foreach ($intros as $intro) {
-				$navNotifications[] = $this->formattedNavNotification->createFromIntro($intro);
+				try {
+					$navNotifications[] = $this->formattedNavNotification->createFromIntro($intro);
+				} catch (HTTPException\NotFoundException $e) {
+					$this->introductionRepo->delete($intro);
+				}
 			}
 
 			if (count($registrations) <= 1 || $this->pconfig->get($this->session->getLocalUserId(), 'system', 'detailed_notif')) {
@@ -242,7 +247,7 @@ class Ping extends BaseModule
 						new Uri($this->baseUrl->get(true) . '/moderation/users/pending')
 					);
 				}
-			} elseif (count($registrations) > 1) {
+			} else {
 				$navNotifications[] = $this->formattedNavNotification->createFromParams(
 					$registrations[0]['name'],
 					$registrations[0]['url'],
diff --git a/src/Module/OStatus/Salmon.php b/src/Module/OStatus/Salmon.php
index 0d393afcce..f928e308d5 100644
--- a/src/Module/OStatus/Salmon.php
+++ b/src/Module/OStatus/Salmon.php
@@ -66,11 +66,12 @@ class Salmon extends \Friendica\BaseModule
 	{
 		$xml = Network::postdata();
 
-		$this->logger->debug('New Salmon', ['nickname' => $this->parameters['nickname'], 'xml' => $xml]);
-
-		// Despite having a route with a mandatory nickname parameter, this method can also be called from
-		// \Friendica\Module\DFRN\Notify->post where the same parameter is optional 🤷‍
 		$nickname = $this->parameters['nickname'] ?? '';
+		if (empty($nickname)) {
+			throw new HTTPException\BadRequestException('nickname parameter is mandatory');
+		}
+
+		$this->logger->debug('New Salmon', ['nickname' => $nickname, 'xml' => $xml]);
 
 		$importer = $this->database->selectFirst('user', [], ['nickname' => $nickname, 'account_expired' => false, 'account_removed' => false]);
 		if (!$this->database->isResult($importer)) {
diff --git a/src/Navigation/Notifications/Factory/FormattedNavNotification.php b/src/Navigation/Notifications/Factory/FormattedNavNotification.php
index 2b1360eaa4..9813fbf859 100644
--- a/src/Navigation/Notifications/Factory/FormattedNavNotification.php
+++ b/src/Navigation/Notifications/Factory/FormattedNavNotification.php
@@ -28,7 +28,7 @@ use Friendica\Model\Contact;
 use Friendica\Navigation\Notifications\Entity;
 use Friendica\Navigation\Notifications\Exception\NoMessageException;
 use Friendica\Navigation\Notifications\ValueObject;
-use Friendica\Network\HTTPException\ServiceUnavailableException;
+use Friendica\Network\HTTPException;
 use Friendica\Util\DateTimeFormat;
 use Friendica\Util\Proxy;
 use Friendica\Util\Temporal;
@@ -73,7 +73,7 @@ class FormattedNavNotification extends BaseFactory
 	 * @param Uri       $href
 	 * @param bool      $seen
 	 * @return ValueObject\FormattedNavNotification
-	 * @throws ServiceUnavailableException
+	 * @throws HTTPException\ServiceUnavailableException
 	 */
 	public function createFromParams(string $contact_name, string $contact_url, string $message, \DateTime $date, Uri $href, bool $seen = false): ValueObject\FormattedNavNotification
 	{
@@ -115,9 +115,9 @@ class FormattedNavNotification extends BaseFactory
 	 * @param Entity\Notification $notification
 	 * @return ValueObject\FormattedNavNotification
 	 * @throws NoMessageException
-	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
-	 * @throws \Friendica\Network\HTTPException\NotFoundException
-	 * @throws \Friendica\Network\HTTPException\ServiceUnavailableException
+	 * @throws HTTPException\InternalServerErrorException
+	 * @throws HTTPException\NotFoundException
+	 * @throws HTTPException\ServiceUnavailableException
 	 */
 	public function createFromNotification(Entity\Notification $notification): ValueObject\FormattedNavNotification
 	{
@@ -141,10 +141,20 @@ class FormattedNavNotification extends BaseFactory
 		);
 	}
 
+	/**
+	 * @param \Friendica\Contact\Introduction\Entity\Introduction $intro
+	 * @return ValueObject\FormattedNavNotification
+	 * @throws HTTPException\NotFoundException when the contact record couldn't be located
+	 * @throws HTTPException\ServiceUnavailableException
+	 */
 	public function createFromIntro(\Friendica\Contact\Introduction\Entity\Introduction $intro): ValueObject\FormattedNavNotification
 	{
-		if (!isset(self::$contacts[$intro->cid])) {
-			self::$contacts[$intro->cid] = Contact::getById($intro->cid, ['name', 'url', 'pending']);
+		if (empty(self::$contacts[$intro->cid])) {
+			if ($contact = Contact::getById($intro->cid, ['name', 'url', 'pending'])) {
+				self::$contacts[$intro->cid] = $contact;
+			} else {
+				throw new HTTPException\NotFoundException('Contact not found with id' . $intro->cid);
+			}
 		}
 
 		if (self::$contacts[$intro->cid]['pending']) {
diff --git a/src/Protocol/Diaspora/Repository/DiasporaContact.php b/src/Protocol/Diaspora/Repository/DiasporaContact.php
index ac8d200aa8..1669707b92 100644
--- a/src/Protocol/Diaspora/Repository/DiasporaContact.php
+++ b/src/Protocol/Diaspora/Repository/DiasporaContact.php
@@ -234,6 +234,18 @@ class DiasporaContact extends BaseRepository
 	 */
 	public function updateFromProbeArray(array $data): Entity\DiasporaContact
 	{
+		if (empty($data['url'])) {
+			throw new \InvalidArgumentException('Missing url key in Diaspora probe data array');
+		}
+
+		if (empty($data['guid'])) {
+			throw new \InvalidArgumentException('Missing guid key in Diaspora probe data array');
+		}
+
+		if (empty($data['pubkey'])) {
+			throw new \InvalidArgumentException('Missing pubkey key in Diaspora probe data array');
+		}
+
 		$uriId = ItemURI::insert(['uri' => $data['url'], 'guid' => $data['guid']]);
 
 		$contact   = Contact::getByUriId($uriId, ['id', 'created']);