Ultimaker S5 stops after leveling, cannot abort, plate doesn’t cool down

[amjaksic 0]

I’ve been experiencing problems with UMS5. I am printing PC and PVA on Wham Bam flexible build plate coated with PC magigoo adhesive. Currently installed firmware is 6.5.3.

 

Once I send a job (via wifi) it starts normally: The plate heats up, print cores heat up, autoleveling of both cores starts and finishes. At this point the build plate should normally lower to about the middle of the Z and print head should move to center front, then the plate should move up and extrusion would start. However, the print head moves to home and the build plate lowers. The display now shows “Ready to print” and the app on my phone says “Finished After 14min” and nothing is printing or queuing. The buildplate does not cool down and stays at 110C. There are no prints to abort, so the plate stays hot. Queing new prints doesn’t help as they never rech beyond “Preparing” phase. Also, I cannot abort the new job. I cannot leave the printer unattended with a hot build plate overnight so I turned it off forcefully using the turn off button. When I turned it back on again, now the app gets the message “Print failed” and the printer’s display shows the same. I’ve done a full reset and after that the first print successfully finished. But the next one failed again as described above (print head homes and platedoes not cool off until forced shutdown). 
Does anyone know what’s happening here and how to fix it?