They have warned about this before, but it’s still pretty wild to think they’re now removing old DMs (and chats, but it’s not like anyone used those).
Interestingly you can still see them if you take out your data via a request, so they got them in the database still.
Are you sure they didn’t give warning? I completely stopped visiting the site when they announced they were taking my app away, but I could have sworn I’ve seen mentions that they were building new chat/messages and that old ones would be gone for a while now. Well before any of the current API stuff.