Custom Item Forms Created in v11.4 Don't Show Correctly in v11.5

I created some custom item forms in v11.4.3, applied the necessary visibility requirements, and associated the form with the required Product Class value.  However, since I upgraded our test environment to v11.5.1 the majority of the fields in the custom forms don’t show, even though they are not hidden or discontinued.  If I remove the custom form association then the default Item form details are all shown.  I also tried creating a new custom form (from the default) and, without making any changes for visibility etc, all fields are still not shown.

Is there anything I need to change/reset/correct for custom forms at v11.5?