Got the same problem.
Trying to run this quest Again couse at first time i did rescue beach boy from harppies and though that coused some problems.
2nd quest attempt step by step:
During the trade i had 1st perception abbility check succesull - (the hand gesture)
2nd abylity check failed - the one that let u cought thief at the act of the crime and prevent it.
3rd abylity check succesful - the one that you realize that you ve been robed.
Spoke qith the trader and the robber claiming that hes a guard - he revealed that Mol is his boss.
Going in to hideout by both ways ( hole after the ladder and/or doing Doni interaction with succesfull ability checks then long rest and then investigation and persuation succesfull after Doni reavels rumble entrance )
leads to Mol giving me 10 sec to leave or whole gang runs away. ( no dialog for give me back my stolen stuff )
After saving Mirkon at beach from harpies or after rescuing Arabella from Kaghda or both Mol starts to talk to me but still no dialog option for give me back my stolen stuff
I also tried to just pick the bag / pouch ( there are 2 bags in their cave - not sure in with bag or is it even The bag with my staff - in EA when Mol gave back stollen ilems there where in that bag / pouch ) so i was assuming that might work but still no quest dont end.
No dialog option with Mol to get stolen goods back and finish the quest.
Last idea is to mayby try steal idol to do all the quest for Mol and see will this gona change anything and finish the "Find your Belongings" east.
but tbh seems like bugged a bit by missing that one dialog option
