And just like that, searching for content in all messages is back.
Did they run an experiment on me (and on @Darryn Brisdaz from the comments)? All I know is since it took them months to give it back to me, I mostly stopped using Facebook and I will never write private messages there again unless I have to. I realize they couldn't care less about a single ...
When you block someone, they will no longer be able to do things such as tag you or see things that you post on your timeline.
From Facebook Help Center
When you block someone, they won't be able to:
See things that you post on your profile.
Tag you in posts, comments or photos.
Invite you to events or groups.
Start a conversation with you.
Add you as a ...
One way this could happen is if your friend is using Messenger from 2 different devices and one of those has "Active Status" turned off.
So your friend last used Messenger from an "Active Status: On" device 1 hour ago.
You then send your message.
Then your friend reads the message from an "Active Status: Off" device 20 minutes ...