The bug is even weirder, because it also “spreads” to other drum plugins, like the VProm drum plugin (VST 2.4) when when I have a drum map there, and a drum map on GA… It appears to get triggered when the drum maps are on and you’re in Play or Record mode. When in “rest” mode, it first wasn’t there until I hit “Play”. Once it was there, it didn’t go away until I removed the GA drum maps.
When I remove the drum map from GA the latency is removed from both instruments. I’m on Cubase Pro 9.5.50 on Windows 10. I don’t have this problem on my Mac, Cubase 9.5 or 10.