Is the air filter cover making my engine stutter?

I have a 125 lexmoto Valencia, the engine loses power for a split second whilst we Rev it (on the centre stand) but only when we have the air filter cover screwed in.

It runs fine without the cover!!!<——

With the cover on and being revved, it will sound like it’s lost a little bit of power and then go back to its original power sound, every 10seconds/periodically.

Honestly me and my partner are frustrated and confused.

 

A bit curious that...

if the scooter is stock then there should be no reason why it shouldnt run with the stock air box/lid in place.

if it runs o.k when cold but it happens when the engine is warmed up, maybe the cold start choke is stuck on.