Hello @Anonymous,
Welcome to Autodesk Forum and thank you for your participation for Answer Day.
It's hard to tell without data set but I would like to help you in general way.
Is this happening when you create a stair?
And which version are you working at the moment?
If you haven't updated Revit up-to-date, please update Revit and see how it goes.
And please audit and purge your files (Both Archi and main file) and do the same way what you are doing and see how it goes.
Hope this helps.
Chonghyuk Lee
Product Support Specialist

Chonghyuk Lee