You should be able to get into the 10cm region using single sided ranging, certainly not km of variability.
I found antenna delays tended to add around 70m per device but that depends on the antenna and channel settings. So with no delay calibrations expect ranges to be around 100-150 meters too long.
It’s odd that your clock ratio is moving around that much, the relative clock differences between the two should be reasonably constant unless temperatures are changing.