I don’t have a solution for this, but this looks similar to the bugs Renoise has loading PSP Audioware VSTs in 10.13, and sounds similar to the Sugar Bytes Obscurium VST bug mentioned in this thread too:
We unfortunately can’t see any errors from the plugins here. They just open with a blank UI with no errors. So it’s also hard to fix something here.
I’ll ask the Rob Papen and PSP Audioware crew to have a look at this. Maybe they can give us some hint of what went broken in OSX 10.13. it wouldn’t hurt if you send them a little support mail too to speed up things.
I read that the Bitwig team somehow opens older plugins now with Cocoa GUI instead Carbon, if provided, or something. Maybe that would be a trace to go? https://downloads-eu.bitwig.com/stable/2.5/Release-Notes-2.5.html
“macOS: some old VST plug-ins that have both Cocoa and Carbon GUI will now open windows with the more modern Cocoa GUI”