A very similar situation has happened with me. I have had to redesign the same form like 5 different times. Very frustrating. Recently, I had configured my form, went out in the field and realized that half of my attributes were no longer showing up! Then I came back to my desktop and they didn't appear in FieldMaps Designer either. So I had to redo that as well.
I had also had the issue, that even though I had deleted an element, I was unable to reuse the field name. I try to keep the field name consistent since that is what shows up in my attribute table in ArcPro. Also, I noticed that elements would remain, or even duplicate in the templates. I have not figured out how to edit the template because it is all greyed out. This progressively got worse each time I redesigned the form. So now when I export my data, I have duplicate fields that are out of order (they show up in the template out of order compared to the order I arranged them in the form). The only solution I have is to completely delete the feature layer and start all over.
So no need to worry, you are not alone in redesigning forms multiple times in field maps!!
