I was having the same issue and posted about it here as well. I managed to resolve the issue by uninstalling the default Windows apps that were hijacking the file associations I wanted to change. Here's the post detailing what I did: Solved Last update caused all custom file associations to reset to defaults - Windows 10 Forums
The problem will come back to bite you when the apps are reinstated.. which will happen if you do an in-place upgrade repair install or (probably) there's another big upgrade like 10586.
Which is why I suggest scanning for old version software may help to give a permanent solution:
Winzip (old version) is one program that has been reported as having this effect.
It might be reasonable to think other programs could equally have such an effect.
Elsewhere I've suggested using the free SUMO update checker to scan installed programs and update them where reasonable.
(Use the version labelled Lite or 'nork' to avoid adware - 'Related Knowledge' - otherwise it's the most comprehensive update scanner around)
SUMO sounds very similar to Secunia PSI which I've been using for years. I try to keep my programs as up-to-date as possible, but certain ones are marked as "end of life" (no longer being updated or maintained) or are paid upgrades. Those ones still work on Win10 and I want to keep using them so I put them on the "ignore" list (so they won't be scanned for updates in the future).
That being said, the apps I'm using for opening media files (the file types that are being effected by this issue) are all current versions.
If the next update causes this problem again by reinstalling the apps I removed I guess I can just keep re-uninstalling them until MS addresses this (I won't hold my breath). However, the way they've designed Win10 to be so aggressive, I wouldn't be surprised if a future update purposefully reinstalls the Metro apps and then locks them down so they can't be uninstalled.
It's programs which are not at all obviously related to either the function or the extension that have been found to cause the problem. One game, Winzip (old versions) for example.
Sumo is the most comprehensive update checker I know of, and I've tried a few. It has a huge database, and is much more comprehensive than Secunia in checking for updated desktop programs. It does not address Windows updates.
Downside- you don't get a straight download link - at least not in the free version.
I have gone through all these methods in an attempt to change .jpg file associations to Adobe Fireworks CS5.1. Regardless of how I do it, the file that opens is Adobe Fireworks CS4. Fireworks of any variety needs to be opened using admin mode. When I click on the program to set the file association, it always comes up as Fireworks CS5.1 but never runs when I select a ,jpg file. It is a X86 program, 32 bit as shown below, but win 10 always loads a different version. My system is a 64 bit one. Any ideas?
Please note that MS has admitted a bug in respect of defaults being reset after a recent update which I'll add here. (@Hwalker1 - this is not likely to be relevant to you.. I'd guess your issue is much more specific).
MS admits bug in KB3135173 resetting associations
See this, referring to KB3135173,
Windows 10 Forced Update Resets Default Apps To Microsoft Products - Slashdot
Updategate: Microsoft 'aware' of problem causing app defaults to reset- The Inquirer
- from which came the suggested registry modification.
Fix for "An App Default was Reset" Windows 10 Resetting File Associations (Registry Fixes) - The Winhelponline Blog
However, it would be better (I think) to uninstall the update, and hide it (see the Tutorial section)
I posted this info in the News section some days ago, but it was moved- I know not where.
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