Link element <> is removed from published Upper Forms

After upgrade from Unifier  9.xx to Unifer 15.xx.  I get the message error "Link element <data element x> is removed from published Upper Forms" when I try to change the BP from draft to complete.

The BP is a working BP.  I need to reopen a field to editable and redeploy to production.

The steps I took:

1- In Stage environment  change the BP to draft

2- Change a none editable field to editable field

3- Stag the BP to staging.

4- Change BP status to complete. At this step I get the error above.

I cannot find any solution or information regard to this error anywhere. I appreciate for any advise. Thank you.