Since the knockback/tumble was capped last patch, using Tongue Grab against a flying Hunter results in them landing a significant distance ahead and sideways, rather than directly in front of you.
Probably not a bug, persay.
The tumble change may have unexpectedly allowed the Hunters to regain control sooner since they only have to wait for for their current velocity to fall below their natural movement speed, rather than coming to a complete halt. That means they can use their jetpack thrust to either cut short their tumble and get away, or more likely, do as you have explained, dodge up or to the side and use their tumbling momentum to get further away.
We are working on this and it should be fixed soon! Thank you for your patience!