So, I stumbled upon this via Google. I also ran into the problems the OP described, namely getting notifications from Windows Update stating it was disabled and I had to set up its settings again. This happened several times per day and it kind of drove me crazy.
I'm using Avast Free now and only recently updated from a 2016 build. My current Avast build is 17.2.3419.0. I'm using Win 7 Professional 64 bit.
The other posts in the topic led me to the (newly added) "Game Mode". Avast states that it 'pauses windows updates' for optimal gaming experience. While I appreciated the thought, I suspected this might be related to the problem. I didn't want to completely turn off Game Mode however, so looked for a more specific setting to turn off. And there is one! It is a bit tricky to find if you don't know where to look, but if you navigate (from the Avast main menu) to the 'Performance' tab on the left, then click on 'Game Mode' (with the controller icon) it should show you the games it has recognized. On this screen, click on screwdriver in the top right and it will take you to the settings for Game Mode. Here you can disable 'Pause Windows Updates'. Just to be certain, I also disabled the 'Disable Windows notifications' option at the bottom. I haven't encountered the problem since and will edit this post if the issue still remains.
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EDIT: The problem actually still persists.
Might simply be because my PC needs a restart after changing these settings. Will update again once I find out what's going on.
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Finally, explanations of the different settings in Avast's Game Mode can be found here:
https://help.avast.com/en/av_free/17/performancegaming.htmlI hope this was useful for anyone experiencing this. It is one of those strange things you don't immediately associate with an update of your virus scanner.