Well, I changed the head 0 rings and the compression remained the same, so I have tried a different gauge and it reads 115psi whereas the trials bike now reads 140psi (which is what it should be).
I have pulled the barrel to have a better look and check the ring gap, the crosshatching is still visible in the bore although there are a couple of small wear marks but I don't think they are too bad. The ring gap is .35mm, but the bore is marked in the combustion area above where the top ring is at TDC. I'm thinking this is likely it!
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