What can this be?

This is on my Montmorency cherry tree, wasn’t sure if this was insect related or something else as it was only on one leaf, no insects as of now but of course they could have left.

Hard to tell from the image. Insect eggs usually laid on underside of leaves.
Frass deposit on topside of leaves is usually dark.

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Looked a bit virus like too, it was on one leaf so I can’t be sure. It also looked like insect but there wasn’t anything there like frass or eggs.