metallic debris in oil filter

During 700 hrs oil change i'd found some debris in oil filter paper.  < 10 small pieces - non magnetic  (photo in attachments). less than 1 mm.

at 550 hrs sprag clutch was changes with rear carter opened but in the followingf 100 hrs oil change (600 hrs) oil filter was clean of debris.

I'd had the sospect that the engine had an overspeed and it seems that there is a subtle power loss 

But compression and leak down tests are perfect. Boroscope analysys ok.

can these metal piece came from lifter surfaces? 

or this kind of bebris are normal after 150 hrs after sprag clutch service?