Hi and thanks for the report.
That is one of the oldest and most devastating bugs still around and not able to reproduce.
However since we can’t track down backpacks I am afraid to say that we can’t handle / restore backpack content.
The only thing we can do is restore your player from a certain save game. All progress you have till now would be lost and we would need the exact timestamp when it happened.
Since this is very time consuming we mostly do it if the loss is dramatically high.
Greets
RexXxuS