Ok, I dug out a column, since I have a few for parts, and a multi function switch cause I was curious how the turn switch worked, three parts to cancel the turn switch, at an opening on the tube the steering shaft has a wheel with nubs, the multi function switch has 2 pieces, one moves with the lever, the other is suspended with two small springs, when the lever is moved and the wheel turned the sprung piece is not effected by the turning wheel until it spins the opposite direction, the piece on the steering shaft then pushes on the sprung piece releasing the lever to pop back to center, I would suspect replacing the multifunction switch will fix this problem.
Older cars have a turn switch with two big arms and the steering shaft below the steering wheel had a C shaped collar with a pole that hit the arm when the wheel was turned back and contacted the arm effectively returning the lever to center, simple, effective, and it worked just fine, the 'multi function ' switch made it much more complicated but it still worked effectively.
Again, I think all you need to do is replace the multifunction switch.
Best guess when not hands on.