Cannot "show" previously "hidden" custom field?

[IT development Department]

I have a custom field called "Start date".

This has a global context (All issue types, global context):

It is "assigned" to the "Default Issue screen" for one specific project:

If I use the "Where is my field" Helper. I get this result:

I click the links and on that page. The field WAS hidden. But even after I click "Show" the field is not visible. And the "Where is my field" helper still tell me that my field is hidden.

Now I have ran out of places to look for a configuration error.

Could anyone please point me in the right direction?

[Nic Brough -Adaptavist-]

Are you sure you are looking at the FC named 'Default Field Configuration' and not another one?