A message, sticker, reaction, read receipt, or media couldn't be delivered. Your contact may have tried sending it to you directly or in a group.
Signal uses end-to-end encryption so that we never have access to the contents of the messages you send; as result when a message could not be delivered it isn't clear if it was sent to you directly or from a shared group with that person.
This delivery issue doesn't affect your chat's security but you may have missed a message from this contact and you can ask them to resend it. When they resend it, it would have the original timestamp so the messages may look out of order.
We want our messaging and calling features to work seamlessly at all times. If you are willing to provide information that will help us prevent this from happening again, please contact us and submit a debug log.