My experience has been to bite the bullet and opt for a new ECU failure oh dear, we'd been expecting it - despite the"precaution" of waiting for warning lights to go out before starting the engine.
I firstly approached Fiat and got through to helpful lady (in Albania I believe) who stated that my Buestner 2016 model was "old" & therefore could not expect much!
I persisted and recounted how this was a known and common fault; she eventually gave me a code. (see below)
I also approached the main Fiat dealer in Bournemouth and came come up against very unpleasant man who in turn gave me an unpleasant price to replace the ECU.
I then approached Essenjay, Poole, who confirmed the fault and agreed to fit a replacement under the terms of my warranty (MB&G).
The chap who did the replacement said he'd had a number of these ( surprise surprise!). He also stated that not one of replacements had ever suffered a recurrence. But this is the interesting bit - the serial number for the ECU is now different and.... Fiat now use a different manufacturer! Well, well.
And the code given me by Fiat? - it had no value when Essanjay purchased the ECU from Fiat.
The van has not been out since ( December) due to weather, (house move) oh and a dose of Covid. Hopefully though with spring on it's way we will be out and about again soon. A visit to Poland to see son, daughter in law and family? We'll see!