Sounds like they were assembled wrong.
Tow line should be on the board closet to the boat.
I use folding Cannon plastic boards and they work well almost all the time.
I have pulled one under water in rough seas and made the mistake of taking boat out of gear. The board flipped over on the way up and took off to the other side of the boat when it came up. Tangled the crap out of everything but made for a good laugh from the crew about my captain skills.