Lookup disappears after adding criteria

Lookup disappears after adding criteria

I add a Lookup field.

Sometime later I go to the form and edit the lookup field and add a criteria. On save the lookup field disappears.

If I then go back to the form in editor mode the lookup is back.

BUT, the criteria is not saved.

I cannot add a criteria to a lookup with this behavior.

My application is shared to support.

please advise

tt