Couldn't find anything about this in hotfixes or patch notes, but hex no longer seems to reduce the aggro range of the target. Previously, both hex and rogue sap had the added effect where you could go past the target during the effect. If you stood directly on top of a hexed target, it might put you into combat, but the aggro range was significantly reduced.
Since Wednesday, this seems to no longer be the case. If I hex a hostile target, then move close to it, I get put into combat where I normally would aggro it. This affects some critical time savers in Mythic+, especially in Neltharion's Lair and Darkheart Thicket, but also some optional skips in Court of Stars. It also affects questing in Suramar, where Hexing a costume dispelling guard let you survive some of the quests there. Now, when you drop your disguise, the guards will get in combat and start pulling even more stuff in hex form.
I have not tested if sap has gotten the same treatment, or if this is only happening with some of the Hex variations (I'm using the 'vanilla' Hex spell which turns them into a frog), but I am hoping this is a bug. If not, Hex just became a Polymorph with a cooldown.