Sometimes it happens.
Its nothing like it was on launch though, and it has definitely, massively improved since then.
don't think there is anything much you can do about it.
"Unlucky" I think is the only way to look at it.
I did once manage to get my items back by having someone knock me onto an assignment grid with a super sledge, but the moment you move 1 hex it activates and kicks you to over world map. So you gotta be sure to be knocked just the right distance.
Dunno if it works for core grids though.
Sorry for your loss.