I am having this issue with a 2020 Terrain as well. I took to dealer and paid for the scan, $200.
there result was no transmission problem but a fault in the electronic shifter assembly. They wanted $1,000 to replace it. F' that.
i bought the part myself (online from gmparts direct) and changed it out. (30 minutes)
seems to work now.
(after reading this thread, I realize it started when temps dipped to 15°)