Going back to your first post, why (not that you shouldn’t be able to) do you open a standalone version of Groove Agent whilst running Cubase?
Do you have the same problem if you open Groove Agent within Cubase?
FWIW, on the previous subject of where the settings files are located I’ve just seen that on my system there are folders both for Groove Agent_64 and also Groove Agent Standalone_64. These include xml files which point to the correct location of the vstsounds. If these are somehow incorrect, uninstalling and re-installing may not affect these files.