Hi,
First of all, I would recommend to get in touch with the vendor and ask them to fix the issue, why the plug-in doesn’t pass Cubase test.
When you enable it, it should stay enabled. The reason, why is not enabled again is either the plug-in doesn’t pass neither the very short test or Cubase doesn’t quit properly (crashes during the quit) so the settings is nt stored. One of the reason of the crash could be the fault plug-in.