Given the tempertures we have had recently I wouldnt be at all surprised if waxing is becoming an issue. Not enough to block fuel lines but quite possible enough to clog ultra fine filters.

Of course, it is one of those "Ice Bullet" things, by the time you have got the filter off and in pieces all the "Evidence" will have melted...

In the good old days all you had to do was add a certain percentage of Unleaded to the diesel (IIRC On my VW T3 the recomended figure was up to 30% in really cold weather) though I doubt if that would be such a good idea nowadays!

Ahh, the benefits of modern technology...