We have a customer who is getting "An entry with same key already exists" error on Equipment object navigator > PM action page and Functional object >spare parts page. Whenever they get the error they delete the “ColOrder” value from user profile and that solves the issue. 

But the problem is after some time they get the error back. They have no idea on what kind of behaviors cause this error to be back. They are looking for a permanent solution for this. What could be the reason for this error to reappear? 

I have already referred below thread but it does not mention any reasons for this error to reappear.