Can anyone identify what is the issue with this leaves?

[Krone]

Prunus mahaleb leaves. What could be the issue? Fungus or bugs?

 

[Wires_Guy_wires]

Stinkbugs make holes like these. But there are microbes that can do the same.
Usually when the infection is caused by microbes, the tissue develops necrotic edges (brown, yellow, black). Because the microbe wants to spread and the plant wants to stop that from happening, so it kills a bit more tissue around the infection.
In this case, that doesn't seem to be happening. So my guess is bugs.

 

[Jzack605]

Shot hole fungus. Common on Prunus.

 

[Shibui]

I agree with shot hole.