Countershaft nut coming loose

Hey peeps, about a month ago i fitted a 520 sprocket /chain conversion kits to mah 09 zx10 and torque'd everything up to specs as per the manual..
Today after a decent ride in the rain i decided to wash the bike and relube the chain etc and pulled the front sprocket cover off to find this..

I didnt use any loctite as the manual didnt state to, and i made sure the washer was locked off nice and flat against one of the faces on the nut.. What would be causing this to happen?
Should i hit it with some medium strength loccy? I just dont want it to be a prick to get off next time round..
Any help would be apprieciated

whatever you do, do NOT loctite it.

you will never get the bastard off.

I'd tighten it up a little more, then fold 2 edges of the washer over.

Yeah was thinking the same wattie.. Its just got me paranoid as fark now! I dont wana have to keep checking it..

if you get it tight and fold over 2 edges - you won't have to worry about it. Always fold 2 edges on these locking washer.....

Thanks for your advice, im gunna fit a new washer and bend the 2 tabs over I was going to do this to start with, but only did the one cause that all that was bent over from factory

and remember to bend it at a point that is as close as possible to the nut, curling the edge over to touch the nut won't have the same resistance to turning as the full flat of the washer being held against the face of the nut.