Had similar issues on original setup of the same groupset. Deeper investigation with most diligent bike mechanic identified a very convoluted Shimano 21-step multi-orientation process for bleeding of this particular R8K hydro brake set. Could be that the tech is using general principles in trying to bleed the system instead of following the extensive Shimano procedure. I've had no issues since this was carried out on my brakes. Note that I have two separate bikes with this same group and both now work flawlessly despite me transporting them inverted from time to time.
Edit: Reason given for the more finicky process was the unique and compact shape of the 8000 brake hoods.
Last edited by SkepticalOne; 01-02-20 at 09:10 PM.