I'm having the performance / graphics performance issue for the last 3 betas. Currently running GM, but this happened with 17a358a and 17a360a all the same. I don't know for sure if rebooting after a sleep/wake fixes it for me, but anything doing accelerated graphics makes the system extremely laggy. It's not beachballing, but the mouse pointer becomes 'detached', where it loses the acceleration settings and just moves over the screen with highlights/labels/selections (when click dragging) following behind with quite the delay.
It's really strange, as I can't always reproduce it, but when it happens it's always when running a few tabs in Safari, FireFox or Chrome with one or more video players, or there is an app that uses OpenGL directly open, like a game (StarCraft 2) or a 3D model viewer. This is on a MBP 2015 13".
Some applications have a little bit more crashy behaviour, like Terminal crashing when you close all tabs quickly, instead of it quitting. But that's probably due to beta data collection/beta program diagnostics. No corruption or dataloss whatsoever. While the beta isn't perfect or anything, compared to the betas for 10.5 back in the day it runs great!