Ipad Message Sync not working

So, after having it a few years, my iPad storage is suddenly full with 21.5 gb of messages. On my phone it’s 2.4gb, iCloud says 53.5 and I have an extra 50gb left in iCloud.

After realizing, I went through some settings and realized message iCloud sync was never turned on for the iPad, so I did. It seemed to work at first, by the next day messages had dropped to 17gb and I was fine to wait awhile as long as it was slowly freeing up space. But now my storage is full again and I don’t understand why. If it was offloading messages, why would it redownload? Is some other setting making them download?

I don’t want to delete messages. Is this just an issue with iCloud sync? Or is something else making all the messages download?