+1, I'm having the same issue.
Wasn't able to find the hideout (failed the Investigation check) so, knowing that if I help the kid tiefling at the beach that I'd get access that way, I pressed on.
Helped the kid at the beach, got the "Investigate The Beach: Find Mol" objective when the kid told me to give the passphrase to enter the hideout.
Went to the entrance, gave them the passphrase, Mol thanked us and rewarded us and then gave me the new quest to steal the idol.
But the "Investigate The Beach" quest wouldn't go away or complete. Talked to Mol about 4 more times to see if I could get it to complete and it wouldn't work. Figured it might go away if I steal the idol for some reason and complete that quest instead?
So I stole the idol, gave it to Mol, she rewarded me and...nothing. The stupid "Find Mol" objective was still there. It still is.
