This sounds very much like the same issue I am having recurrently on my 2019 P Elite. Happened again last night. I have talked to the dealer a couple of times about it but to no avail. the scenario is as follows;
1. have Fob, get in drivers seat.
2. Driver Door Closed
3. In Park /Brake Pedal Applied
4. Push Start /Stop
5. All instrument and Dash lights illuminate, Speedo and Tach go full range, return to "0" (indication to me that everything passed self test, (my guess anyway)
6. Instrument panel appears normal
7. No START response what so ever.
8. Instrument Panel responds with " To Start, Press Brake Pedal and push Start /Stop (Already Done step 3 & 4 Above)
9. Pushing Start / Stop ONLY turns all POWER OFF
Wait a bit and repeat above and will start.
IMPORTANT NOTE Wife has indicated to me that the Brake Pedal does not depress as it does when it works normally (indicates its hard). Initially I thought this was just her not understanding the difference in feeling of the brake when the engine is running (boosted brake) and when it's off. However, she has since told me that she can predict when it isn't going to start before she even tries it by the feel of the Brake pedal.
Last nights incident happened as usual, and had been about 6 weeks since the prior time. The indications were all the same as indicated above. She also indicated the Brake Pedal Pushed Hard at this time. After she tried the sequence again with no success I decided to take a look under the dash and see if I could see the brake light switch (Not sure whether that is what controls the signal for "Brake Pedal Applied" during the start sequence or not) or to see if there was another switch on the brake mounting that may control this. I could not see any of the switches but decide to try this instead. I initiated the above start sequence again up through step 8, the Instrument Panel responds with " To Start, Press Brake Pedal and push Start/Stop. I pushed harder on the brake pedal by hand and the giggled the brake pedal side to side 3 or 4 times while still holding it down. Then pushed the Start / Stop switch and it started normally.
I spoke to the dealer service writer today about this and queried him as to whether the brake light switch is a SPST (Single Pole / Single Throw) switch or if it could happen to be a DPDT (Double Pole Double Throw switch. He indicated that it was a single SPST switch that controlled both functions, Brake Lights AND Brake Applied for Start Switching. I wasn't sure that was the correct answer so I did a little investigation on the switch itself and found that the direct replacements being sold at parts houses are DPDT. Now knowing that there is more than one function that has to be controlled with the Brake Pedal Application, ( at least 3 I can think of off the top of my head, 1. Brake Lights, 2. Brake Applied for Start, and 3. Cruise Control Cancelling ).
My suspicion is that this switch may be the culprit and have an intermittent contact in it or a misadjustment that is causing the starting malfunction. Not having all the Schematics and Theory of operation of this system limits how deep I can go on diagnosing this problem.
My next move is to have the dealer check it out in the near future and talk directly to the technician if possible, or wait for the issue to happen again and see if Jiggling the Brake pedal again solve the issue.
If you are having a similar issue I would suggest trying the Jiggling the Brake pedal and see if it lets the vehicle start