EGS (6 speed robotic gearbox) on C4GP 2l Petrol

[jnoam]

First, apologies. Im a newb here and hope I am not doing something wrong, and thanks in advance for any help you can maybe offer.
My issue: a 2008 2.0l petrol C4GP with EGS gearbox. Owned the car since it was new and it was great, with no major repairs (and 210,000km).
Recently I got stranded a few times when the gearbox got stuck in gear. An example is - driving comfortably in "A" mode. Gearshifts become slow and in less than a minute the display changes to "2" (i.e. manual mode) but paddles can change gear so OK and arrived safely at destination. Next time wanting to start the car the gear is stuck at "4" and refuses to start ("Select N" on display). Wait a day or two and it goes back to normal.
Took it to the shop, they recalibrated the clutch and it drives better when it does; but did not fix the problem.
I checked the hydraulic liquid level, no problems there; took off the sensors - they look like new and perform well with a multimeter. Visually inspected (as much as possible) the wiring harness towards the ECU, no visible faults there.
Any ideas on what I should check?

I watched this fantastic video - on which I based my testing so far. But I am as stuck as my gearbox now. Any ideas?