Why has the range of movement of the control surfaces changed over the past year?
We found the problem. The control stops are under the seat and are made of plywood. It looks like at some point in the past someone had added a small layer of plywood to reduce the control deflections but that over time the glue had deteriorated or the wood had swollen, so that there was now too much stop. Removing the extra ply and sanding the glue back to the wood fixed the problem.