VAGfan

The oil jets are for piston cooling, not lubrication.
And from what I read in the Self-Study Guide (description of all the technical details of the EA888 Gen-3 engine), it is a fail-safe configuration, with a separate oil pressure switch to detect failures. It seems that the engine will protect itself from damage if a failure is detected. Based on that, I don't think that a failure of the oil-cooled-piston system was the root-cause of any of the above engine failures.

Monitoring the function
When the piston cooling nozzles are activated, the contact in the oil pressure switch,
level 3 F447, closes. The switch is at the end of the oil gallery for piston cooling nozzles
(see page 26, figure 606_003).

The oil pressure switch can detect the following defects:
• No oil pressure on the piston cooling nozzles despite request
• Faulty oil pressure switch
• oil pressure in spite of the deactivation of the piston cooling nozzles

The control valve for piston cooling nozzles, the following electrical faults can be
detected:
• cable cut, piston cooling nozzles always enabled
• Short circuit to ground; cooling off piston
• Short circuit to +; piston cooling always on

In case of faults causing the piston cooling does not occur, the following backup
reactions are triggered:
• torque limiting and speed by the engine control unit
• No level of low oil pressure in the control oil pump
• There in the instrument cluster display a message that the plan is limited to 4000
rev / min, a beep, EPC warning light.