On civicrm 5.20.1 under WordPress, we have added two custom fields to the Registration Info profile (gid=12). We've added that profile to the Online Registration config for one event.
Now and then, for reasons unknown, those fields will stop displaying: on the online registration form, and in the profile preview. Flushing caches (with
cv flush or with the "Cleanup Caches" button at
q=civicrm%2Fadmin%2Fsetting%2FupdateConfigBackend&reset=1) causes them to reappear.
Then sometime later, they disappear again, until caches are again flushed.
I've verified that neither the profile fields nor the custom fields are being disabled, nor are there any changes in user permissions, ACLs, profile config, custom field config, etc. The only corrective measure is to clear caches.
Is this a known issue in any 5.x version of civicrm? Naturally we're working toward an upgrade to the latest security release, but it would be nice to have some reason to believe that such upgrade might also address this mysterious issue; or to have any other way to address it besides periodically flushing caches.