If you change your account or don't play YouTube for a long time, Disable Loudness Normalization will be disabled.
This can be fixed by temporarily must be disabled and re-enabled.
Confirmed.
I found that sometimes YouTube also needs a hard refresh (Ctrl+F5). I suspect this might be when YouTube is opened at a time where the extension hasn't fully loaded yet or something.
If you change your account or don't play YouTube for a long time, Disable Loudness Normalization will be disabled. This can be fixed by temporarily must be disabled and re-enabled.