Did you put oil inside the filter before closing it up or leave it empty ? Some people fill the canister then insert it I never know if that's the norm or not...
in see, this van van blocked the oil filter oil inlet hole and reroute it through the oil cooler, which is how aftermarket oi cooler kit mod works for non oil cooler version of this engine
if you look closely it's not complete blocked, just restriced to a very small hole, to bypass the oil cooler at high rpm, i guess. taking note, i'll will modify my gn125!