Does Facebook sometimes block the ability to search for private messages?

It seems Facebook completely dropped my support (but not for other people I know) for searching for messages. I can only look for conversation names (persons, pages or chat group names) or search for messages inside a specific chat.

This directly contradicts what Facebook’s official support states, and as mentioned it does work for other people. It doesn’t work for me in any browser.

Any idea what causes this and how to fix it?

This is how it looks like now:

Search Facebook chat titles

If I choose a specific chat, I can search by clicking “Customize Chat” first, although what does search have anything to do with customization? It’s as if they don’t want people to know search is possible within a specific chat:

Search in a specific chat

And this is how they (used to?) search inside specific conversations:

Search for Facebook messages