Whenever the Serum2 UI is open and there are animated elements, the Renoise UI starts to stutter and the Serum2 UI stutters as well. I know that Reason 13 had similar issues and they’re currently tweaking their VST3 implementation in the latest beta because of that. Apparently, the Xfer developer is in touch with the Reason Studios devs about it. There’s a demo version of Serum2 available, so it should be reproducible with that. Not sure if this is just happening on my end or if it might be a more general issue.