Pretty weak on Apple's part removing iCloud iMessages tbh.
Syncing issue.
Mine appeared to sync but not across all devices. Only a combination of reducing save messages from forever to 30 days, going to manage data, and deleting the message data, deleting each remaining message, and then a couple times of rebooting the device and deleting any messages that popped up kinda cured my issues. In the end, the newer messages seem to sync across devices but the sync date stamp was stuck in mid July.
It will return, hopefully fixed.