Merge pull request #54031 from nextcloud/backport/53922/stable30

Author: provokateurin

apps/federatedfilesharing/lib/OCM/CloudFederationProviderFiles.php

@@ -281,7 +281,10 @@ private function shareAccepted($id, array $notification) {
 
 		$this->verifyShare($share, $token);
 		$this->executeAcceptShare($share);
-		if ($share->getShareOwner() !== $share->getSharedBy()) {
+
+		if ($share->getShareOwner() !== $share->getSharedBy()
+			&& !$this->userManager->userExists($share->getSharedBy())) {
+			// only if share was initiated from another instance
 			[, $remote] = $this->addressHandler->splitUserRemote($share->getSharedBy());
 			$remoteId = $this->federatedShareProvider->getRemoteId($share);
 			$notification = $this->cloudFederationFactory->getCloudFederationNotification();