When Micro Focus moved from UFT 14.03 to 14.5x, they removed the UFT4WinRT service due to it causing instability issues with Windows 10/Server 2016/2019. It almost sounds like your instance is still looking for this even though it shouldn't.
Try this: if the affected machine has the following registry key, delete it:
HKEY_CURRENT_USER/Software/Mercury Interactive/QuickTest Professional/MicTest/AddIn Manager/WinRt
Based on your description of your environment, it sounds like your Citrix deployment might be using shared profiles that's holding on to 14.03's registry information. That is, make sure you are cleanly upgrading to 14.5x/15.x with no 14.03 file or registry remnants remaining.