AC/Heater blower wont turn off

The air-conditioning blower will not change speed or turn off in my 2015 SV. The heater and AC work properly and produce hot and cold air. The issue is the blower which runs at a constant speed. When the fan speed is adjusted there is no change. When the AC is turned off the blower continues to run. When the car itself is turned off the blower continues to run for about 5 - 10 seconds before switching off. The blower immediately turns on at the same speed when the car is turned back on. Any thoughts on what is causing this issue?

That's a new one by me. I assume that it's the blower speed control, but that's just a guess.