Ah, very nice catch!
When investigating your game in more detail I see that the item is a level 1 item, but placed in a level 3 ruin. This messed up my logic in the code, i.e. the level 1 ruin that respawned didnt realize that the item was already taken by a lvl 3 ruin.
Code updated and I hope this is the last we see of this issue!
Thanks a lot for your detailed info!