Intermittent alarm message – saturated particle filter

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In December 2016 the fuel tank was filled up and the car was driven about 6 km and parked in a garage. After 2 days of not being used the car couldn't be started. The authorized workshop quoted that the fuel tank was filled up with bad quality fuel. For this reason, the fuel injectors and fuel pump were replaced by the workshop.
After 2 months the car couldn't be started again. Fuel quality was tested and no issue found. We filed a claim that the car wasn't diagnosed and fixed correctly for the first time in the authorised workshop. Now the authorized workshop quoted that the diesel fuel was frozen (despite the fact that the car was parked in a garage). The workshop continued in searching for further causes, presented different excuses, wanted to replace the fuel injectors and fuel pump again. I refused this without having a test report from a test bench showing that the fuel injectors are defective.
The workshop called several days later that the car starts normally without any issue. The engine ECU software was flashed with an update of the emission system. The car was returned and after driving only about 50 km a warning message that FAP filter is saturated activated in the instrument cluster. The filter saturation value was 75% and after cleaning it dropped to 12%. The car had 128 000 km on the odometer.
In February 2018 a message that the diesel additive was low turned On. The diesel additive was filled up at 160 000 km.
In June 2018 the warning message "that the particle filter is saturated" with DTC P1490 stored in memory activated. This fault issue was diagnosed by an authorized workshop (at 164 000 km). A month earlier the car passed its regular MOT without a problem!
Further diagnostics (at non-authorized workshop) of the DPF system, function and level of saturation and the fuel injectors were tested again. No issue found.
The warning message turned On again later and this time a different FTP filter was installed just for trial purposes. The warning message also turned On with this different filter. The catalytic converter was inspected with a camera and no issue was found. The differential pressure sensor was replaced and a HELLA sensor was installed. The warning message on the cluster keeps turning On and this happens at different intervals that can range from 100 km, 500 km and sometimes even 2 000 km.

September 2018 and about 170 000 km when the warning message activated quite frequently. The vehicle was placed in an authorised workshop with the workshop saying that the front part of the FAP filter is blocked despite the fact that the pressure values are good and the filter saturation is only 23%. The workshop recommended filter replacement. I had a discussion with them that all figures are indicating that the filter is not saturated. A new OEM filter was installed and after driving about 2 000 km the warning message and DTC P1409 reappeared again. A warranty repair claim against the workshop that the issue was not fixed. Fuel injectors tested and some were replaced, a glow plug was replaced and the diesel fuel additive fluid was replaced. In January 2019 the engine ECU software was updated with no issue until June 2019 at 183 000 km when the warning message activated together with the DTC P1490.
The vehicle was taken to a non-authorized workshop where they quoted that the message and DTC are present but otherwise the vehicle is OK and they have no reason to work on the car. The car was taken to another authorized workshop where they said basically the same and that all values are OK. They cannot determine the exact fault cause or defective component. They said that some component is most probably partially defective but they cannot say which one at this point. They told me that I should drive the car and that something will eventually fail and then they will know.
I don't drive the car for only short distances so I think that the car has the correct conditions for particle filter regeneration.