My messenger is okay now. I once in awhile deactivated my facebook but when I reactivated, my friends can no longer send me messages saying "this person is unavailable in messenger". I watched something in Tiktok on how to fix it. Hope this will help to some. Just long press the person you can't message then select archive, go to your profile on the upper left screen and choose archived chats, long press again the person then select unarchived.