ECU EDC15: Intermittent Starting Problems

Hello, I'd like to briefly introduce myself. I'm a vehicle electrician and service technician.
I often browse this forum when I need something.
Okay, now I have a question myself.
I have the following problem.
I have a SEAT car here that belongs to a friend.
The data is above.
The car is running relatively well.
Okay, no problems. But sometimes it doesn't start.
And if it doesn't start, it won't start at all.
The car won't start, so I went to check it out.
Immobilizer: everything is okay.
Read with VAG-COM, tachometer. Error: Intermittent communication failure with the engine control unit.
Engine control unit read; no response.
Tried again. Then suddenly, an error message appeared: "Engine control unit locked."
Okay, everything is deleted. The car is running again.
Three days later, the same problem occurred: the car wouldn't start.
This time, I removed the immobilizer from the engine control unit to eliminate any issues related to the speedometer and the wiring between the speedometer and the engine control unit.
Car 3 is running again.
Three days later, it stopped working again.
That time, I picked it up myself and drove it.
Always bring my laptop.
And suddenly, I want to start.
It won't start.
"I used VAG-COM to read the engine data, and there were no error codes, but then it suddenly started working again."
So, I continued driving, but the problem occurred more and more frequently and could no longer be resolved even by communicating with the MSG (presumably a system or device).
So, my question is: is the control unit defective?

Search function, relay 109 checked?

Sure, I replaced the relay first.
The problem remains.
It's strange that it works when you access the control unit via the diagnostic interface.