iMessages disappeared and then reappeared after reboot

I’ve looked but not seen this covered elsewhere. If it has please point me to the relevant article.

I have an iMessage thread with my brother, who is also in the Apple ecosystem. Earlier today, five months of the most recent messages on that thread disappeared. This was on both my ipad and iPhone.

I sent him a message, on the same thread, and asked him when was the most recent item from me? He responded that he got a note from me this morning. Clearly our threads did not agree.

I rebooted both my iPhone and iPad and all of the “missing” messages showed up.

Does anyone have thoughts on what happened?

• thanks