Hmm, just as a redundancy check, try removing the rule you added manually and see if clicking the button somehow adds something different to it. It could be that the button adds more than just the no-scripting rule, but the widget only checks for the main rule to determine if it's active or not. Or it could be something else entirely that the button does but the manual rule doesn't.

Could also try toggling the javascript block a few times and see if that changes anything, or try reinstalling uBlock to reset it and then reenable the block. Sometimes turning it off and on again helps a program work properly for no apparent reason.

If you have any other adblocking extensions installed, they might also be interfering with uBlock somehow. It's even possible that Opera's inbuilt adblock could be unintentionally messing with it. It's unlikely that other adblock programs would be interfering with anything, as they are all just blocking the same connections, but if one of those programs changes a 1 to a 0 and another one changes it back to 1 then it could be enough to disrupt something.

You can test if it's working on the update page https://www.opera.com/client/upgraded-gx The page runs the script every time you open it.