I am working on an nginx environment (not sure if it’s relevant, but just more detail). I resolved the issue by reinstalling ACF and now all fields function as normal.
To be more clear, all the fields I was trying to update or remove were created in v.5.5.14 and it was individual fields within a group that would not delete. Also, the field table layout seemed to break after the first time I saved by adding the “Key” column and forced “Type” to return onto a second row of table headers – these new columns couldn’t be removed with WP’s Screen Options.
