I’ll take a look when I get chance (hopefully this week some time). In the meantime…
I think the problem here is that cubase/reaper aren’t using the Windows 10+ per-monitor resolution support that Cantabile is using. Cantabile does this to allow Cantabile’s UI to be hidpi and plugins to be mixed/scaled up.
Does the plugin appear correctly when hidpi and/or upscaling is disabled?
Brad