We have recently found that the client-side portion of the hotfix is already included in UR3, but some of the DLLs were further changed with UR3.
This can lead to a situation where installing the client-side hotfix after UR3 will load an older version of three DLL files (DesktopMFC.dll, EssentialsDB.dll, RevitDB.dll), and the other changes in UR3 were not meant to work with those older DLLs. This is where we see the error above when launching Revit.
To clear the issue, restore the DLL files by renaming the 391388 appended version (e.g. DesktopMFC.391388.dll) back to the original file name or replace the DLL with the ones below: