Hey! Thanks for feeback! You can try talking to Shaartan and this may end the quest or you need to fully restart the game and it may fix the stones so you could close them again. If it wont help the problem also could be resulted due to reloading the game while doing this quest... so you might need to start new game or just continue w/o finishing this quest.
Have same problem. Got the quest, Killed spiders, Used Strength to block the spider nest, but in questbook the spider nest block is not marked as done. This is probably a bug (if fixing via hotfix, do please try to make it so it checks if the nest is blocked or not and then marks quest correspondingly (or resets the nest if the quest was not completed))