There is a recent issue I have noticed with Nightblade characters. In some circumstances, if you cloak while standing, then crouch while already cloaked, it takes you completely out of stealth. I haven't been able to isolate the exact contributing factors that cause it, but it does seem to happen quite often when I'm cloaked and then crouch as I'm passing enemies. So, pretty much the exact moment you would NOT want to come out of stealth.

From a logical standpoint, there is no reason for this to happen. I suspect it is a byproduct of a recent (intentional) change that takes you out of stealth and uncloaks you in certain situations like swimming.

As for why I would crouch while already hidden, my main uses a speed stealth build based on Night's Silence (no speed penalty when crouched) and Darloc Brae (restores resources while crouched), so I benefit more from crouching because the resource gain offsets the magicka drain of using the cloak. I typically cloak to quickly enter stealth when needed, then crouch after to get the resource buff. It was never a problem before, and it seems to have happened around the same time that swimming started removing stealth.

This is on PC NA.