Try to find someone with a PIWIS - maybe a local independent Porsche racecar mechanic. You may have to update the firmware in the brake controller. I'm pretty convinced this is a firmware issue in the brake controller.

I learned my lesson the hard way about this Service Mode, but fortunately the car was still under original factory warranty when it happened. It took they guys at the dealer nearly a week to get it calibrated, and they ended up replacing both actuators and the brake controller unit.

 

The car is still under warranty, and I think you're right. There's something wrong with the firmware, or the third-party scanner has limited reach. I'll report back here once this is resolved. Thanks for prompt response.

 

Should be zero issue. I have cycled it on/off when doing brakes and it works fine. I'm not sure you even need to put it into service mode to do the rears, just release. I used the scanner to go on/off to disable the brake. Odd people are having issues.

 

Next time, I won't modify this function. Which type or brand of scanner are you using?

 

Xtool d7

 

I managed to get the car out of Parking brake service mode using a more advanced scanner than I had used before. This needs to be coded if you're converting from Steel to PCCB.
Thanks to @fourthirteen for mentioning the Launch X431 scanner, as it was the only one that worked for me.