I have a number of custom fields with this same issue....
I have used (numerous times) the "Configure Fields" button on the issue edit screen to add additional custom and built in fields to appear on the Edit Issue screen. However, this selection does not seem to stick for the custom fields - I frequently (daily? Not sure) access the edit Issue screen only to discover that that the custom fields are not visible. I add them by checking them via the "Configure Fields" button, and all is well - until tomorrow when they are no longer there, and I have to add them again.
Today, I thought I would try "Where's my field" before just re-adding them. An example is the field "Buyer", which is a custom field of type User Picker (single user). Here is the info provided by "Where's my field".
It says the field should be present, which it will be (temporarily) if I tick it...... What am I doing wrong???? Why won't it (and its custom brethren) STAY on this screen?
PS they appear and work just dandy on the main Issue screen, of course only visible if there are content in them, which is why they need to appear on the Edit Issue screen....