Windows 10 Taskbar bug presented in 1709, worst on 1803 upgrade

1. No they are not the same icons that disappear, but it does appear to be dependant on the order the icons were displayed in.  Note: I'm still not sure but I think the zorder issue and missing icons issue may be the same and icons that are "missing" are just outside the avalible zbox. In other words the box is too small and cuts off icons. I belive this since the apps are still running and upon scaling and resolution changes they sometimes come back leading me to believe they were never really gone just obscured from view. 
2. My current work around is to use always show icons. Using always show icons fixes problems 1, 2, and  3. But not 4 which is blurry icons. 
3. I can easily recreate the problem on any machine now. While using scaling, change resolutions trying multiple different scaling and resolution settings. Various different combinations will generate each of the different issues seen in people's screen shots or combinations there of depending on your original settings.
4. Blurry icons seem to be a separate issue from the other three but I have not yet conformed.  I haven't done as much testing on the blurry icons. 

I hope the above helps and while for you changing scaling  from 150 to 175 and back works for you it will not work for everyone as the native resolution and scaling and the variation of the scaling and resolution changes seem to all contribute to various combinations of the problem.

If I had to narrow the issues above down into one I would say it is a notification box size issue as windows seems to try and format the icon spacing and location based on the size of the notification box. Some times the box is too small (missing icons) or too big (padding) or off center (below start bar).  I think of they fix the box size then items 1-3 all get fixed. 

I hope my testing notes above help.

Regards,

Bryan

Thank you Bryan, I think the notion that the first three issues boil down to an inadequate size of the overflow window rings true.

That does remind me of a couple of more things worth mentioning:

• Changing the display scaling manually, sometimes generates a message that says "Some apps won't respond to scaling changes until you sign out." I think we need to be clear that we are not making display scaling changes intentionally when the problem happens - a game or app may be doing that as part of resolution changes.
• Jason asked me to grab a screenshot of the overflow window with transparency set on the taskbar, to see if the overflow window was getting displayed behind it. The answer to that question is no, as evidenced by the below screenshot. I think this also reinforces your notion that the problem is simply the size of the overflow window not being sufficient:

about the blurry icons, as someone mentioned, it doesn't happen to ALL icons, however, MOST icons are affected. also, it is not reserved to some 3rd party apps.

for me, the only icons that are NOT AFFECTED are:

• task manager status icon
• network status icon
• battery icon
• volume icon

icons AFFECTED:

• windows defender notification icon (white shield with green checkmark badge when no issue)
• IDrive
• every other 3rd party app i've used

1. it only depends on current order of notification area icons
2. that is the "workaround" i use. i check "always show all icons in the notification area" to avoid losing access to icons after resolution switches. i never have an icon disappear this way.
3. in my case, to repeat the issue, i just have to start a game that uses 1920x1080 resolution and quit. upon returning to my 3820x2160 200% scaling desktop, the overflow notification area is scaled improperly and some icons cannot be accessed anymore. the overflow box ends up extending behind the taskbar.

Bah I do not know the most stable version was the previous one this April...

This is NOT a complex issue. You fix something like this in 20 minutes work of programming. They could even do a quick and dirty workaround, of just resetting the frame if you switch resolutions. They wont fix this. There are bugs like this since beta of Windows 10. For example, if you flip a tablet into tablet mode and switch landscape mode, there is a high chance, that the task menu date is shifted ut of the screen and you cant see it anymore. They never fixed this too, where it is easy to fix.