There are Youtube videos (just Google search) on the proper procedure for draining/flushing/filling coolant and bleeding air out of the radiator for BMW (also applies to other modern cars). Just in case, I check the coolant level over the next few days.
https://www.carcarekiosk.com/video/2.../flush_coolant
The X1 F48 coolant capacity is ~7 litres, so you should know if the radiator is not full.
I had suggested the air lock problem in post #18.
https://f48.bimmerpost.com/forums/sh...7&postcount=18