Have broken reed petals while the engine is turning over at 12,500 rpm, back of the piston munches the reed to carbon powder and disappears out the exhaust. But for the missing reed you will never know.
Maxima 927 is good oil , no problems with that.On a hard ridden 125 25:1 would be the very minimum of oil I would run. Remember "Nobody killed a 2 stroke with too much oil" (sic 'Spanky')
I see this as a straight mantenance issue, a 125 will usualy need 2 rings to every piston and a new piston would be needed after 15-20 hours on a track as a general rule.If your lifting the top end after season end your asking for trouble.
I would seek a reputable tuner rather than the one your persisting with.
Cranks and big end bearing failures are caused soley by the lack of lubrication.
Learn how to do a plug chop and how to read a plug(you will find you don need your 'tuner' then)
As mentioned cylinders can be replated for about $200 +piston no need to buy a new cylinder.