For those of you who still haven't resolved this hanging/crashing issue with the Messages app, even after upgrading to 10.14.4, to hopefully restore Messages to its default settings -- which means that you will lose any current settings and messages -- you might try entering the following three commands in the Terminal app, which you will find at /Applications/Utilities/Terminal:
NOTE: Before you do this, make sure that you shut down the Messages app first. In fact, to make it a little easier, you may also want to delete all current conversations it contains first, and then shut it down.
1. To delete all of the ".plist" files in "~/Library/Preferences" which pertain to Messages, use this command and hit your "return" key:
find ~/Library/Preferences -name "*iChat*" -delete
2. To delete the cache files which pertain to the Messages app, use this command and hit your "return" key:
rm -rf ~/Library/Caches/com.apple.Messages
3. To delete the chat database which pertains to Messages, use this command and hit your "return" key:
rm -rf ~/Library/Messages
To avoid any hiccups, you may also want to log out of your account, and then back in again, or even totally shut down your Mac entirely and start it up cold, before relaunching the Messages app.
Also, you may possibly have to use the above commands a few times before they take hold.
If even this doesn't work, I am wondering if maybe it is some kind of Apple ID issue, and a conflict between different devices you own where Messages is installed. In fact, whatever the problem is, you may have to fix things on different devices. This could even be an iCloud related issue.
If the above info has been helpful, or resolves your issue, please do let me know. Thanks! :)
