The key you tap to wake up your computer is sent to the focused application, so it's possible the key you hit is increasing the playback speed. Tap one of the shift keys to wake up Windows.
It seems to be the case. I conducted further tests with the opinion.
I played music on MC, then opened one or more applications to put MC into background playing. I even minimized MC. When the monitor went to sleep and I pressed any key to wake it up, the playback speed still increased.
I found that waking the monitor with the mouse did not cause any problems, and not all keys caused the playback speed to increase. (Unfortunately all shift keys increase the speed.)
It appears that I will have to wake the monitor with the mouse until this problem is resolved. Reinstallation after clean-uninstallation couldn't resolve it.
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edit:
I updated to 32.0.47 and retested.
Still not solved. Even mouse waking is now unavailable.
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edit2:
I installed the ROG CLAVIS, an ASUS USB DAC, and tested again. Works well.
It looks like a problem with onboard Realtek sound. My mobo onboard sound chip is ALC897.