I created Releases for the next six months. When I want to add a future release to the 'Fix Version' field, most of the Releases don't show up. This is something new as, until last week, all the releases showed up.
I am not sure if this is a contributing factor, but one of the releases that didn't show up in Fix Version was out of sync. What I mean by that is all our releases are on Tuesdays, but this one was on a Thursday (in error). All subsequent releases didn't show up in the Fix Version.
My workaround was to delete archive past releases and delete future releases. I then created new versions and now they are all in the list. I'm not sure if the archiving of past releases was necessary.