My I-messages (texts) are randomly moving to the deleted folder. How do I stop this from happening before I lose them?

There are at least 11K messages in the message thread. I attempted to delete all of the messages a few weeks ago then changed my mind and decided to recover them. Now there are about 3K messages that automatically move to the deleted folder every other day. How do I stop this? I have plenty of space on my phone so not sure why this is happening. And I do not have I-messages (texts) set to delete after 90 days or 1 year. I have it set on keep forever.