Undetectable status is alerting survivors with visual TR, chase music, and stingers.
PC - Undetectable shouldn't be causing stingers, visual terror radius, or chase music. I'm assuming this is a bug, as it doesn't make sense otherwise. Undetectable shouldn't be giving off a visual heartbeat, for example. Video below. If by chance this is a feature, it's gutting the ability to actually sneak up on survivors.
Hard to say how the stinger happens, but I suddenly hear chase music a lot when I'm following a survivor while I'm stealthed - even if they are unaware of my presence and not looking at me.
Edit- new footage of the bug. See my reply below for the two timestamps