Thanks for your help, Eve. In Windows 11 it looked a little different, but when I scaled to 100% the problem remained. (although it looked a bit smaller 😉)
That's unfortunate it didn't fix it. It is seeming like it's either an HL Convolver bug 'directly' or related to how hosting a VST within your audio application is implemented.
I've mentioned elsewhere, odd alignment / UI issues on VSTs in JRiver before. The thing is, those can crop up in pro audio applications too so it's not like JRiver is to blame here really?
It's not a 'fix' exactly but MetaPlug has been consistently helpful at sorting out VST issues for me. It's actually the only way I can get WAVES stuff working in JRiver reliably. It's a VST host itself so occasionally it can work around problematic VSTs.