Does anyone know what’s going on here, and if there is a fix to this?
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The detail about your soil being clay tells us a lot. At first sight the light green in the leaf indicates maybe a deficiency of some kind, but on clay soil that is highly unlikely. An easy test is that peach trees like a soil that is slightly acid; if the pH is wrong then this can tie up nutrients that are otherwise plentiful in the soil.
Clay can lead to poor drainage. Peach trees need to have positive drainage, preferably on a deep sandy soil. Periodic flooding can be detrimental to the root system which gets reflected in the leaves.