Facebook deactivation led to block all of my mom's contact on Messenger

Hi everybody,

So yesterday my mom told me she had enough of Facebook and didn't need her account anymore but wanted to keep messaging her contacts. I gladly told her that it's doable as I've done the same 2 years ago. I then took her phone and deactivated her account and deleted the Facebook app on her phone, all while she was there.

What happened next is super weird. On my Messenger app, when I tapped her photo to send her a message the following message appeared "this person is unavailable on messenger" or something like that. Impossible to send her anything except a video or audio call. Same happened on my brother and dad's phone. We decided to reactivate her account, uninstall and reinstall the app, both for Messenger and Facebook but nothing fixed the problem.

Finally, I decided to uninstall and reinstall my Messenger app on my own phone and everything went back to normal (but only for me of course). My brother and my dad had to do the same in order to send messages to my mom. The problem is that now, all her contacts (a few hundred FB friends) are having this "This person is unavailable on messenger" message.

It's super weird, I have myself deactivated my account a while ago and nothing like that happened. Thanks in advance for the help!!