Yeah, it's the "completed" ones that seem to be the problem. If they still have a star next to them, some of them get into a state where they're stuck and not properly flagged as completed. Once they're clicked on the quest completion message often pops up again and then party banter resumes. I'm not sure if it's necessary, but I do the same with the codex entries too (though it's often a pain trying to find the ones that have updates) as the same thing happens there too. As far as I can tell, it's just the completed quests getting stuck in limbo that seem to block party dialogue.
Seems my list of stuff to check on when I get back to Skyhold is gradually lengthening: check inventories for best items, check upgrades, sell stuff I don't want except for stuff I collect which goes into my fancy new chest, think about crafting new items, turn in creature parts and what-not, check requisitions, chat with anyone who needs chatting with, tick off any codex and journal entries I've missed. Argh! Memories of the infamous locker shuffle in Mass Effect. Though it's still not quite as bad as that.