Malfunctioning Exhaust filter

I have a 2015, RR Vogue 3 litre which I have owned for about 18 months. No issues until this May when the 'exhaust filter full contact dealer' red warning light came on and the car went into limp mode. Took it to my local independent LR garage who flushed it through and all was well. About 1k miles later the light came on again and again took it to the garage and they flushed it through and told me there was nothing wrong with it I just needed to drive it more at higher speeds! Now I have literally done another 200 miles and the light is back on and the car is in limp mode again. I now don't really trust my usual garage any more and the LR garage will cost a fortune so any advice? There is another independent garage locally but not sure the car will even make it there - will cars make a 5 mile trip in limp mode? I usually drive about 100 miles a week and at decent speeds. I have seen a local company which specialises in ECU and DPF solutions so not sure if they are worth contacting to have a look, thanks for reading.

If any doubts with the dpf itself, it should be removed, tested and cleaned professionally.
It is a consumable item unfortunately and at expense.
A few things to bare in mind with a dpf.
They can crack inside due to blockages and overheating.
The wrong engine oil,
Defective pressure sensor and it's pipework,
Short journeys and age.
I hope you get it sorted