@petrscruff Have you heard back from Apple on this? Also, your example project is missing files I think. It fails to produce the error you're showing here.

I only have the issue when debugging @IBDesignable views from IB. It just doesn't work (and hasn't for a long time), and fails with this error. Debugging the app in the simulator works fine for me.

And beta 3 makes the situation even worse. It's going the wrong way here. I've sent tens of gigabytes of data on this issue and I've got no response while the system gets gradually less usable as we move towards release.It's kind of pathetic. Would it really be a crime for Apple to let me know what's going on here?? I'm commiting significant time to getting this nonsense fixed and the silence is deafening.

After a couple of days with 10.15.4 beta 2, it appears it makes these crashes far more frequent. At this rate, I'll be forced back to Mojave quite soon.