Whenever dire avengers "reload" and you use their grenade it won't work until the weapon cooldown is over, moreover, the unit will be stuck in place and then launch the grenade after a while.
Could it be intentional or does it seem like a bug? They're reloading so they don't have a spare hand for a grenade?
I've encountered this as well, it doesn't make sense from balance pov as you're losing control over units abilities when main weapon is disabled.
Their grenades should be their backup for when their weapons go into cool down mode. Definitely a bug.
It was a bug and is solved now