Fatal error when trying to manage display

I ran into the same problem today.
In my case the reason was that the field referenced by the formatter was removed.

Same here; I had deleted a field that was referenced by Display Field Copy. This resulted in entity forms running into a fatal error.
Removing the ds.field.[field_name].yml and running drush cim fixed it.

Maybe field copies should have a form of dependency on the original field, so that they get removed together with it?