I have created some custom fields to collect size data as part of an event registration form. When I first create the fields I am able to include them in a profile and use them on the form. At some point though the profile becomes unable to display them and nothing appears. A regular profile preview just shows an empty box, but if I try to preview a single field in the profile then I see the message "This CiviCRM profile field is view only".
I have not found any way to make the fields display again. If I create new ones and use them, they will work for a while and then stop.
The further mystery is how they could be broken after a time? A scheduled job? Most of the enabled tasks are "always" and so I would not expect the form to work very long at all (cron runs every 10 minutes on this site). I wonder about the "clean-up" task since it runs hourly, but I'm at a loss to imagine how that would affect custom fields.
Any thoughts folks?
Running 5.31.1 on Wordpress 5.5.3