For some reason I can't get the extension Admin Columns to work. I have the TGM activation in place and seems to work fine.
Other plugins, like Include Exclude, work fine. But Admin Columns does not.
What am I missing?
Oh, I see your custom code set a column show and you have a custom field with the same ID. Then you set that custom field displayed in admin columns, which already exists there. It might be confused. I'd suggest removing your custom code and try again.
As said, this code works fine for one CPT, but doesn't for another. Only difference between both are the funcion-titles and post-type names.
Could it be caused because of a earlier error where something is going wrong in building or filling a database table?
What makes me think that is when I rename 'suppliers' to 'sponsors', I get the same issue.