Just watched a u tube video and there was a gent who spent a small fortune trying to have his van fixed (blocked filter.
Turned out to be the external temperature sensor in the offside mirror was missing (a fiat dealer had fitted a replacement mirror and it didn't have a sensor in it, just a hole where it should be) easy to check if it's there just a hole if it isn't of course, you could have a sensor there but just not working, in true fiat tradition, you just can't buy a replacement sensor.
Apparently, the filter will not regenerate without the sensor. once the mirror was replaced and the filter cleaned ,it worked