Hi I'd check the groove in the piston now where the circlip sits. The design in the piston is for a round form clip, the one on the left is a square form.
Hopefully it hasn't damaged the seat so you can use a proper wire type one.
Can the one on the left, get a proper wire type one and if the piston groove is marked, get another piston.
When they come out at 10000rpm they make a hell of a mess in the barrel, the piston is cheap by comparison.
Never ever use a square form clip in a round wire groove or vice versa.
Always use new clips, and always put a rag in the crankcase until they are in and seated. You can never get the buggers out if you drop one in to the crankcase......
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