An internal Messages error occurred. (tried everything)

This occurred when I upgraded to Mojave. Given that I have not seen similar Mojave-related complaints, but have also seen complaints about this with previous OSs I am gonna assume this isn't a problem specific to Mojave, but not sure.

Nearly every time I open Messages I get the error pictured below "An internal Messages error occurred. There was a problem with Messages. You need to quit and open Messages again."

I can usually get it to open if I go through this a couple times. But once I'm in messages, my conversations (which are synced to iCloud Messages) are not shown the same as on the phone. Commonly I will receive a message on my phone along with a notification on my Mac, but when I click it on the Mac, the conversation doesn't open in Messages, and I can't find it in the list.

I have deleted every iMessage preference file indicated on other forums, deleted library/messages, signed out of messages completely, disabled and re-enabled messages in the cloud on both my iPhone and Mac, and cleared my PRam for the heck of it.

Please send a (working) iMessage from the heavens and tell me what to do!!

2017 MacBook Pro 13" w Touch Bar, Mac OS Mojave 10.14.