Nothing flat out broke, but I am developing and dogfooding on a Mac, so I get visual QA for free on that platform. When I tested my app on a Windows machine, I noticed several UI regressions that looked/felt really janky. I didn't get as far as testing a Linux build, but I assume I'd find more issues there.
I can't remember why I wanted to migrate to 2.0 now, but there was a nice-to-have that I couldn't do in 1.4. I ended up abandoning the 2.0 migration after a slew of cryptic errors, took a step back, and decided I'd be better off using Electron for my project. My app is at heart a rich UI text editor and none of the computation is that expensive. With all the value add coming from the interface, optimizing for consistency there feels right.
Interesting you ran into UI regressions on Windows. I'm looking forward for us to get to that point where we can test on a Windows and see what changes...hopefully it's smooth.
With Electron's UI powered by the same browser across platforms, you end up with a much more consistent experience. Makes sense to optimize for that.