Ok - I've done some sensor findings and basic process of elimination.
Firstly, I want to correct what I posted above (I've now updated my post). #20 is the EGR temp sensor for the additional EGR cooler (left of engine). #19 is the EGR temp sensor for the main EGR cooler at the front of the engine. The BMW parts diagram is a little confusing.
This is the secondary/additional EGR cooler temp sensor, circled in yellow, including the connector. Left of engine (as you face the car):-
This is the main EGR cooler temp sensor & where the connector is:
To access both these sensors, I removed the engine cover, airbox & pipes, unplugged the MAF sensor. The main EGR cooler temp sesnor connector is at the back towards the bulkhead under the sound insulation.
Results.
1) Unplugging the secondary temp sensor, did not put an EML on the dash, however it stored the same error I had been receiving and at the current mileage. Also, BimmerLink would not clear the code with the sensor unplugged. I plugged it back in, cleared the code. Unplugged again to confirm.
2) To make sure its wasn't the main temp sensor, I disconnected that. It gave me a drivetrain error on the dash (and display), but also an EGR error as well on BimmerLink:
Summery - I'll order and replace the secondary EGR temp sensor and hopefully that solves this intermittent issue. Part #20 - 13628574358
https://shop.bmw.ca/a/BMW_2018_X5-35...s/13_1539.html
I'll come back and post once I've done this and confirm if it did indeed fix it.