Quoted from YeOldPinPlayer:

A good place to ask would be the Avengers club thread. https://pinside.com/pinball/forum/topic/all-hulk-get-is-tilt-avengers-club
Might be helpful to post a photo when the ball is stuck on top of the target. Take off the glass, start a game, manually drop the target and put a ball there. Maybe the target is dropping too far and getting stuck on the lip of the playfield?
For your Loki lock problem verify you have exactly six balls in the game. Check Loki lock switches 49, 50, & 51. Check trough switches 17-23. Does this problem happen specifically on a particular lock? i.e. after the first ball is locked it malfunctions, but on lock two or three it always works properly?
For the ramp it sounds like the angle is too steep. Is something loose at the top, screws backed out or something raising the top or maybe the ramp bent a little?

Quoted from pinballaddicted:

Our Hulk had that issue. That issue is not in any thread that I could find. Save the Hulk threads to your favourites. You are going to need them!
There are a few things you can check. When the ball is in the shooter lane, the auto plunger needs to be touching both sides of the ball and centred so it shoots the ball straight. The plunger must not be touching the ball. This will ensure that the ball gets auto plunged to the top of the ramp each time. You may need to bend the auto plunger to suit.
When the plunger strikes the ball it must hit centre and slightly top side of the ball. This gives the ball top spin and shoots it straight up the ramp. This could be where your issue is. The plunger is not hitting the ball in the correct spot or the correct angle. Make sure that you have a green plunger spring fitted as per standard. If the machine has a red plunger spring it will continuously hit that ramp no matter what you do. It was a lot of mucking around for us but now that we have it sorted machine is awesome.
If you are unsure you can video the plunge and auto plunge on your phone and play it back slo mo so you can see what it going on. Everyone that bought an Avengers LE had some sort of issue. This is why it is rated so low. Most owners sold them as is so nearly every machine out there still has some sort of issue or another.
Killer game if you can dial it in properly. We have sold other more desirable machines according to others but our Hulk has been managing to make the cut every time!
Good luck!