After several attempts of the following.
- signing in and out of all devices
- turning on/off icloud
- turning on/off imessage
- multiple restarts on all devices
- rebuilding the iMessage data on the mac
- time machine restore
- ccc restore
- countless hours on reddit, forums, google searches
the conclusion I reached, there’s something off about Mojave and iMessage sync. If I turn off and disable all devices (Message>Preferences) from the Mac (because for some reason, it won’t allow to disable only “this” device) then everything begins to work normal again. But since it turns it off on all devices, I go back to my iPhone and turn on the iCloud sync again, which automatically re-enables the mac iMessage sync via icloud again, and then it breaks, gives an error, quits, and removes recent messages.
I heard in the Apple forums that this is supposedly fixed in the Catalina Beta, they have been aware of it since Mojave was released, but haven’t provided fixes, probably because not many users experience this error. I am not willing to mess around with a beta on my mac. I can wait till the final release.
For those who have this error, if you ever have additional fixes, let me know. But I hope the info helps out for anyone who has the same issue.