This is really weird, as this problem appeared out of nowhere yesterday. None of the airports have any parking positions, except BIKF and PHNL, which are included in FGData. I have this problem with version 2020.3.6. Any fixes ?
UPDATE: I just tested with 2020.3.8 and 2020.4.0 (I have them installed all three, but each version has its own FG_HOME and FG_DATA folder) - the parkings for these versions ARE GONE TOO
Update 2: I've got my parkings back now - see this thread's last post for more information !