If you're talking about
[Visor Enhance I], if you aim down your scope the module highlights enemy players with a red aura, similar to tagging. This aura shows up even while stealthed, making cloaks far less useful. If the tag-aura and tagging are linked, you may be able to evade this sort of problem by equipping
[Blind Spot II] with visor tag immunity. It's untested and unconfirmed though so don't rely to heavily on that advice.
Additionally, you don't need to be 'visible' for enemy players to properly tag you with their visor either, sometimes even accidentally tagging you as they scan the scenery. An observant player can spot distortions made by the cloak which gives you away too, though running around your opponents in stealth is trickier to spot by eye.