Each time I loot a buoy, nothing drops. The buoy disappears as normal. Per a historical bug in PC I walked completely around an island looting 20 or so entry buoys until they started respawning. All new ones were also missing.
Currently in zone D7, but I first noticed empty buoys in C7.
come to think of it, I have not seen a map drop since getting wiped out (buffed) while entering F6 (see other bug posting)
Single player world