Help with ABS issue

Hi guys, so I recently purchased a 2016 sonata hybrid, looks great and had a brand new battery. However, the brakes were funny at first. I would step on the brakes once and it would stop just fine, however when I would step on them again within a short time, the brake pedal would not go all the down and stop the wheels unless I stomped on it. It begins to feel as if I have no brake pads. I went to multiple mechanics who could only scratch their heads, unable to diagnose and fix what was wrong. Finally, while driving, the ABS warning lights came on. After many failed mechanic solutions, we finally went to the dealership. Surprisingly they themselves do not know what is wrong with it…and it is quite racking up the bill. Has anyone had this problem and found a solution to this braking issue?

some details of the work already done:
-Previous owner of the car had ABS unit replaced at their dealership prior to me purchasing it.
-my first mechanic bled the lines and checked the calipers. No change
-second mechanic replaced the ABS unit, brake master cylinder, and bled the lines again. No change
- finally we took it to the dealership who has been working on it for a month now, and they changed the ABS, master cylinder, and bled the lines simultaneously AGAIN. This effort has racked about $5K, and it seems that even this work was futile.
If anyone knows what else, aside from the aforementioned parts, that could be the problem please help out.
-Thank you!

 

Usually when the ABS light comes on there is a code to tell you where to look, do you know the code?
How many miles on it? It could be a bad wheel bearing, or wheel sensor. even something as stupid as a brake light switch, or bad tail light bulbs.(or led bulbs in place of standard) The code would narrow it down.

 

I don’t know the code, but it’s at about 83,000 miles. We went to the dealership to figure this out but I guess they didn’t catch the code either