Had a similar problem on Spirit just this month. I can get on and off the plane fine, but I need a wheelchair to get to and from the gate to the curb.

In Portland, got a chair from the counter to the gate, no problem. Was assured a chair would be waiting in Vegas… no chair.

I had to hang around the gate until they figured it out, but there was no way I was getting from the gate to the cab stand on my own.