button does not work

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I have also heard of some weird behavior being fixed by just removing the green Raspberry Pi Compute Module and then re-inserting it to make sure it's fully seated.

Also, could you post some photos of your circuit board? That could, potentially, help us figure out a problem.

Did you try the evtest or jstest?

Porcinus is right, gpio readall (or gpio allreadall) would also be a good test.

Try this.

Release all buttons
Run 'gpio allreadall' and take a screenshot, photo, copy/paste, or whatever of the output.
Hold the A button
Run 'gpio allreadall' and take a screenshot, photo, copy/paste, or whatever of the output.
Release the A button
Run 'gpio allreadall' and take a screenshot, photo, copy/paste, or whatever of the output.
Hold the B button
Run 'gpio allreadall' and take a screenshot, photo, copy/paste, or whatever of the output.
Release the B button

Let us know the output from that. Perhaps this will also help us understand the problem.

Thanks!