Default apps always change and/or reset (many usual solutions tried)

Hi,
Running Windows 10, creators update, so version 1703 and build 15063.332. The update history shows KB4020821 installed back in May, and KB4020102 installed this month. Also some "Click-to-Run Update Support" was installed this month, and the malicious software removal tool was installed last month.

For the past two weeks or so, I've had the same problem that many have had. The default apps for pdf, epub, html, mp3, avi, mp4, and so on, get reset. Html and epub are always going to Edge, the others go to the programs MS has deemed appropriate (Outlook 2010 changes to Mail and so on). This seems to always happen when I reboot, but sometimes occurs after several hours of using the computer, without any specific trigger. Sometimes the "App default was reset" messages appear, sometimes not.

I've tried to switch back to the software I normally use (the latest AcdSee for pictures, WMP or MPC-HC for media, Firefox or IE for Internet, Sumatra or Adobe Reader for PDF) using all the methods, from changing them from Email/Maps/Music Player/Photo Viewer etc. to changing them from "choose defaults by file type", "set defaults by app", or by right-clicking a file and choosing the program that way.

I tried the registry hack from 2016, which didn't help. Then I tried the Powershell commands, removing some of the default apps. Now Groove no longer hijacks the mp3-files, but the mp3-files don't stay associated to WMP or MPC-HC, either. They go from WMP to "unknown". I have no old versions of WinZip or nothing like that (an old WinZip was often mentioned as the source of the problem), and haven't had problems before. I just suddenly got a bunch of "App default was reset" messages, and it's been fun ever since. I have McAfee Total Protection and WinPatrol running in the background, but disabling those didn't help. I'm the only user of this desktop computer, and don't use Microsoft account to login. The "email, calendar and contacts" have one MS Account with my e-mail on it, no other accounts there.

I don't know what to try anymore. Are there any programs or solutions that would save the default apps once I have put them how I want them, and could then revert the changes Windows makes? Or are there some other things I could try? I have naturally scanned the computer for malware using several different software, used "sfc /scannow" to check for file integrity, and so on. It just seems that the apps always reset to MS defaults (or to "unknown", if the default software is not available) during a reboot, and often after using the computer for a few hours. As someone who does a bit of photo and video editing and often has to click on web and mailto-links, this is a real pain. Any suggestions would be greatly appreciated.

Thanks for the reply. I have tried to uninstall pretty much every software there is, including McAfee and AcdSee, but no use. Sometimes WMP stays as the media player, but the browser still always changes to Edge and Outlook always changes to Mail.

I used msconfig to disable all startup items, and several services, rebooted, and the change still occurred. Then I rebooted to Safe Mode, switched the app defaults, and rebooted again to Safe Mode, and even then Edge and Mail became the default apps. I tried that about a dozen times (rebooting and staying in safe mode), and that happened each and every time. WMP sometimes stayed as the default player, sometimes it asked me to choose an app. AcdSee or Affinity didn't stay as picture viewers. Sometimes Windows Photo Viewer became the default, sometimes it asked be to choose a default. PDF also always switched to Edge, regardless of what PDF viewer is installed.

As you said, this is something that seems to occur with certain configurations and with certain updates. With me, the problems have occurred just these past weeks, but some have been searching for a solution for well over a year. I tried a program called SysTracer, took a snapshot, rebooted, took another snapshot, compared the two, and got a 1126 page pdf which I can't understand anything of. Well, there are parts like these:

Hash
REG_SZ LZrlGW0IPSQ= old
REG_SZ NA4sBsCg4vo= new
ProgId
REG_SZ ACDSee Ultimate 10.png old
REG_SZ AppX43hnxtbyyps62jhe9sqpdzxn1790zetc new

The "AppX43hnxtbyyps62jhe9sqpdzxn1790zetc" is apparently Photos, so I know something is resetting the defaults, but what? No idea. If I uninstall ACDSee and replace it with some other image viewer, it just changes the "old" values. I'll try SysInternals ProcMon next.