Valkyrie's tactical is bugged
Valkyrie's tactical cannot be cancelled, unlike other legends whose tac ability can be cancelled by either swapping weapons or using melee.
If aiming starts on the ground, the only way to cancel her tac is to use her jetpack.
If aiming is started in the air, there is currently no way to cancel her tac. You are also unable to cancel your jetpack once you started aiming. So the only way to stop is to either be forced to shoot and waste your missiles OR you're forced to wait until your jetpack runs out of fuel.
This is very inconvenient because if you are aiming at an enemy, but then run under cover or into a building, you are either stuck floating in the air, wasting your fuel, or forced to shoot your missiles at nothing and waste them.
Her tactical also shoots accidentally if you are trying to ult when there is an obstruction above.
Please see video in post linked below for examples.
Valkyrie's tactical ability is frustrating : apexlegends (reddit.com)