Front sprocket nut coming loose. Why?, How?, What's the fix?

[map]

Following on from this thread on the Hysung GT125 Comet.

The nut holding the front sprocket has come off again.

So not sure why this is happening, any plausible explanation welcome.
The nut was certainly tight (1 metre breaker bar).

Short of some threadlock loctite not sure how to prevent. More important to know why suddenly occurring (over-tight chain?)
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[Fisty]

A new nut (they are a locknut IIRC and should really only be used once) or a tab washer if there is a groove on the shaft.

Pic of the nut and shaft please.
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Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[Suntan Sid]

You'll have to use thread lock, if there is no lock washer.
It's a common problem on DRZ's, the recommended fix is the correct torque plus thread lock.
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"Everybody needs money, that's why they call it money!"

[Vincent]

The tip I got off someone that races bikes is to use RTV silicon sealer and it worked for me. You'll need to get the sprocket and the end of the shaft spotless first.
The sprocket's not on the R/H side is it?
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Space Is Deep

[Pete.]

Put a flat washer under it.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good