Noticed this today:
GM Program #:
Oct 15, 2019
Enable Diesel Engine Block Heater - Exp. 11/30/2021
Certain 2017 - 2019 model year Chevrolet Silverado 2500/3500 and GMC Sierra 2500/3500 vehicles, equipped with the 6.6l Duramax diesel engine (RPO L5P) and optional engine-block heater cord, may have a condition in which the block heater cable function was disabled.
Dealers will replace the engine block heater and cord.
So it looks like the fix is in.
Now how much you want to bet that the dealers have no parts in stock?
Had mine done this morning. Was in and out in just over 2 hours.