[RichH]

Could also possibly be the result of the fuel oil containing amounts of reclaimed 'biofuel' made from used cooking oils. The chemical responsible would be the contaminant - oleic acid, a well know 'problem' in fuel oils made from and blended with reclaimed 'cooking oil'.
If such is the case, then you will also find that the 'gaskets' and O-rings made from BUNA or Neoprene would be 'softened'.

On most filters with this type of physical configuration, the 'sump' is on the upstream side of the pleat pack; therefore, such flakes and debris would be captured on the pleats, but not the 'dissolved' nor particulated debris that is much smaller than the µM rating of the filter media, but surely would help to 'choke' the flow of oil if and when they did break loose.

 

[RichH]

These are probably made in China by Xingtai Shengkaiyuan Material Co a 'new' manufacturing (a private label / re-branding) firm attempting to penetrate the lucrative worldwide automotive filtration market.

Fleetguard Oil Filter (LF670/LF677) China (Mainland) Auto Filter

 

[RichH]

That's a bit frightening, since there's nothing on the can to indicate where they're made (and I've never questioned why they're so cheap).

I notice they also make 'Volvo-brand' filters! Shiite.. I've been lucky so far but will need to be a lot more vigilant in future.

Volvo has not been a Swedish Company since 2010; and, is now owned by the Chinese firm of Zhejiang Geely Holding Group Co Ltd.

 

[RichH]

Headquarters still located in Sweden but is Chinese owned.

EXCLUSIVE - Boardroom tension mounts at China-owned Volvo - sources | Reuters