Which Tap Forms version are you using? I’m not seeing the crash after I add a new Link to Form field, then click the little x button at the top-right corner of the Link to Form field on the record to choose the fields to display in it.
It crashes when I remove fields. That happens both when I initially change from showing all the default fields to a smaller set of fields, and later when I remove selected fields from a ‘filtered’ set.
Adding fields seems to work fine, though, no crashes there.