Sometimes the Renoise GUI also very shortly freezes and audio continues (no xruns). Never had this before with this PC. This also happens when saving the project, but this seems to be normal as this happened always.
edit: This seems to be because of auto backu, so it’s totally fine.
I don’t know if this is still relevant for people, but I also used to have a lot of problems with vst instruments (especially the u-he ones) on Linux even with Renoise 3.4.3. Sometimes they would just freeze/crash renoise or the GUI would just remain a black window.
It turns out that for some strange reason this issue was related to glibc locales. Installing the glibc-locales packages on Arch instantly fixed all those issues for me. On Ubuntu the package would be called locales-all, I think
Maybe this will help someone who runs into similar issues at some point