I use UAD a lot in WaveLab and can’t think of any issues, though UAD is still VST2 only which I think developers have an easier time with. What’s interesting is that UAD doesn’t officially support WaveLab but they appear to be very stable.
I don’t use Waves very often in WaveLab anymore. The last issue I remember which I believe is resolved was the disappearing cursor.
I also rarely use a Steinberg plugin.
We need to find a way that some of the mid-level developers such as FabFilter, DMG, Plugin Alliance etc are more stable in WaveLab, as well as the smaller or less popular developers.