I've notice on the JJ's with the electric starter; the bendix O-ring sticks to the compressor nut and doesnt retract. This caused the engine to try to spool-up under the drag of the electric motor. This was solved by a little dab of silicone grease on the o-ring and the bendix then shuttled forward and back off the nut without holding back the turbine rotor.

Watch the bendix at cool down, it should move back and forth. A few black marks on the brass bendix ring will show it spining and stopped when the ECU comands it.

The JJ does not have a spring retracted bendix. The O ring is rubber and was binding on the nut. I use silicone grease on my JJ.