Anyone figured out how to get around the sneaking issue with regard to the Rescue at Fort Neugrad?

In case no one knows what this is; When I'm sneaking around Fort Neugrad at night to attempt a rescue of my fellow Stormcloaks held prisoner, I'm somehow detected before I've even reached the fort. I've attempted to approach from four completely different directions and somehow the quest objective always updates with a "Failed to Sneak" message. Mind you, I'm not even in view of any enemies.

Is there some work-around for this bug, or am I just stuck with storming the castle?

The sneak method is for the secret cave entrance.
From the wiki; Follow your quest marker around the fort to the lake. Be careful not to get spotted by any Imperials or you will fail that objective and have to storm the fort. Once in the lake, swim down and you will see a small wrecked boat with a locked chest slightly hidden under it. Directly behind you is the entrance to the cave.

But honestly, it doesn't matter, there's no bonus or consequence of just storming the fort.

I understand what I'm suppose to do, the problem is no matter what direction I approach from, I can't even reach the lake before the quest updates with "Failed to Sneak." I'm not even getting detected. No one is there to see me. It's as if it updates with "Fail" whenever I get within a certain distance of the fort.