Act 4 Runeseeker - Farrow bugged

I can't complete the last(?) step of the Runeseeker quest in Act 4. I did the expedition and even got the entrance for the "Deserted Post" open, but after finishing it and summoning Farrow, I can't speak with him to complete it. I tried multiple time, by opening new instances, but that doesn't help.

Anyone else with a bug in this quest in Act 4 seems to have problems earlier in this quest. Can't find anyone else talking about this part though.

I found a workaround!

My friend was doing the same quest and took me with him. I still couldn't talk with Farrow for some reason, but as soon as he did, I could activate the rune plate to finish it.