I'm working in Jira Cloud and have created a number of custom fields for a particular project. The fields that keep disappearing are in Create Issue screens. When I create an issue the custom fields don't show until I click the "configure fields" button in the top of the create issue screen and check the boxes next to the missing fields. I have to repeat this process every time I create an issue.
I checked the field configuration and none of the missing fields are set to hidden.
Not a big deal to me, but users who aren't very familiar with Jira won't even realize that the fields are missing.