
Try going to the Field Maps Online Map Editor. Seems to potentially fix this issue.
1. Open your map in the online program.
2. Go to Settings for the map
3. uncheck then check again the collect here and copy buttons.
4. Save the map (upper right hand corner floppy disk)
5. Test in field maps app.
I found some limitations though.
1. If you have a feature in your map that allows copying but is not editable, then when you hit the copy button in field maps, it gives you the option to copy that feature to another layer of the same geometry.
2. If you have a feature in your map that is editable, then the only option you have for copying is to duplicate that feature. It does not seem possible to copy that feature to a different layer. Unfortunately for my use, this is a drawback of the FieldMaps app.