Persistent Beachball in Messages

A few days ago, I was chatting via Messages and because the phone I was tethering off of went dead, and I reconnected after connecting to the wireless network of the hotel I was in, which is...dubious at best.

Now Messages isn't working. It loads, I can receive messages via notifications and the unread messages number increments, but any attempt to interact with the application directly gets caught in a beachball, and Messages shows as Not Responding in Activity Monitor, and is taking up 100% of a core. Weirdly, it's persisted past a simple OS reinstall, which is surprising.

Any idea what's going on here, or how to fix it?

You can try and remove the ~/Library/Messages and ~/Library/Caches/Messages folders, then restart.

I had exactly the same problem.

If I went into Activity Monitor it showed messages running at 80-90% of CPU. jI spent hours on the phone with Apple support and they couldn't figure it out and recommended I take my 27" iMac to the apple store. This is after I had done a full recovery "restore" that supposedly over-write the OS. Well it must not

Ugh! Really didn't want to drag this big thing to the apple store but I did and they ran all the diags and there was nothing wrong with the hardware. They recommended wiping the disk and re-installing the OS.

In a last ditch attempt to avoid spending a week trying to recover my environment I went into Time Machine and restored the messages App from a week or so before the behavior started happening.

That fixed it immediately. I didn't even have to restart. My CPU usage went from 90% to >10% when idle... which is in the range it should be. Not sure why but somehow I suspect that the messages application itself to corrupted.