PTO won't start mower deck

I'm having an unfamiliar problem with a John Deere E170, purchased in 2019. Started earlier this week when mowing. The mowing deck stopped operating. No odd noises, no squealing of belts, just stopped operating. Nothing blocking the blades or belts, everything seems to be there. I stopped, started, tried reengaging the POT, with no luck.

I just went through all the steps above in the solution listing below, and all operate normally (i.e, shut off when it is supposed to, stays running when it's supposed to). The engine runs normally, starts easily. I followed every step exactly. Twice.

I can engage the engine, drive from point A to point B, but the mowing deck will not engage via the PTO. Any other ideas for this? I don't want to have to take it to the shop if it's something I'm just overlooking.

Adding: All the connectors are tight, wires are unfrayed and unbroken. There are not obvious issues with any of the connections or wiring harnesses. The tank is full of gas.

Many thanks in advance. Here's what I tried, gleaned from another question from a few years ago:

Testing Park Brake Switch

1. Park machine safely. (See Parking Safely in the SAFETY section.)

2. Sit on seat.$

3. Unlock the park brake.

4. Try to start engine.

Result: Engine must not crank. If engine cranks, there is a problem with your safety interlock circuit.

Testing Park Brake

1. Park machine safely. (See Parking Safely in the SAFETY section.)

2. Lock the park brake.

3. Try to push machine manually.

Result: Park brake must prevent machine from moving. If machine moves, parking brake needs to be adjusted.

Testing PTO Switch

1. Park machine safely. (See Parking Safely in the SAFETY section.)

2. Sit on seat.

3. Lock the park brake.

4. Engage the PTO switch.

5. Try to start engine.

Result: Engine must not crank. If engine cranks, there is a problem with your safety interlock circuit.

Testing Seat Switch

Test 1

1. Start the engine.

2. Move throttle lever to maximum speed position.

3. Unlock the park brake.

4. Engage the PTO switch.

5. Raise up off seat. Do not get off machine.

Result: Engine should begin to stop. PTO should shut off immediately and mower blades should stop.

Test 2

1. Disengage the PTO switch.

2. Start the engine.

3. Unlock the park brake.

4. Raise up off seat. Do not get off machine.

Result: Engine should stop. If engine does not stop, there is a problem with your safety interlock circuit.

Test 3

1. Start the engine.

2. Lock the park brake.

3. Raise up off seat. Do not get off machine.

Result: Engine should continue to run.