Nope, can be a good hint to uninstall gsx and install again? Should include all the last fix and update
Reinstalling won't make any difference, since the installer still must rely to the updater to get the latest fixes. I can only repeat and confirm I'm unable to replicate the problem.
Also, I've asked several details, but you haven't answered, so I'll repeat them again:
Please indicate the precise, exact, sequence of what you are doing, because the I can only confirm that now, choosing anything that results in stairs moving ( Operate Stairs, Boarding or Deboarding ), works fine.
Also, please provide more information about the airplane used. How many stairs it has ?
And, provide more information about the parking spots. Is this happening only on a parking you customized top add passenger waypoints, or everywhere ?