The thing I notice is that I hear the performer out of sync via the monitor. The one time it worked, I heard them in sync.
What you mean “via the monitor”? Do not engage track monitor for Performer tracks even if it is possible.
“Cuabse crashed” - could you send a crash log? And did you restart? People sometimes refer to “crashed” when they mean something else like hung, or partly crashed, so, sorry for the silly question 
Also, some more info about your systems would be helpful, Win/Mac, Cubase version, audio interfaces, buffer size etc. Furthermore, this may help to understand delay issues etc: https://helpcenter.steinberg.de/hc/de/articles/360012899079-Troubleshooting-for-VST-Connect