Same thing happened to my 2019 Ram Rebel last night. Drove home last night during a winter storm. Had the truck in 2WD drive most of the way, then 4WD. Upon returning home tried to put the truck in park and the info display kept displaying... service transmission and it wouldn't let me turn the truck off and stated it was not in park and that I needed to engage the emergency brake.
Saw my 1st 2019 Ram on the road other then mine yesterday 7/10/18. I saw a red Longhorn on 07/12/2018. Saw my 3rd on 7/31/2018. Saw my 1st off road package besides mine on 8/5/18 which would be the 4th 19 Ram I have seen now