Hi WayneWWW,
I moved the discussion to a new topic: Jetson Nano SD card enters back to high speed mode instead of uhs mode after soft reboot. The solution provided above does not solve the issue. Basically it is for a different issue - the person loses his dtb changes on a reboot, which is not the same in my case. In my case the SD card switches to a low(er) speed mode (details in the next forum) on soft reboot and it is a coincidence that the speed it switches to are the same as before my dtb changes, hence the confusion. I can always get back to the high speed mode (as intended by the dtb changes) by a hard reboot, and I have no clue why this behaviour is different in both the reboot cases.
Besides, the changes in patch provided in the link in the answer above is already present in the the L4T sources (32.2) I have.