UPDATE 2:
The issue was we changed damage volumes on team bases so they now eliminate enemy players instead of damaging them.
This creates an issue with join-in-progress because when players load into the island they have no team assigned for 1 or 2 seconds, which makes them instantly die due to spawning in either team base.
Now, this triggers the Save Point device and saves this instance of the player when they’re not fully loaded yet, saving an empty inventory. This essentially wipes players inventories.
So the error was mine, however the fact that the save point device saves the player before they’re fully loaded is the 4 year old bug I was referring to. This has made most creators give up on saving loadout entirely.