Since a few days, suddenly Windows 10 forgets every file associations. I've tested png files, txt files and avi files.
I had that happen with 7Zip in Windows 10 but not in Windows 7; running the program as administrator in 10 made the associations stick. Are you talking about Windows 10 proper or a program within Windows 10 such as 7Zip?
I'm talking about Windows; the file types that I mentioned earlier, I had already associated them to their programs, but Windows sometimes forget those programs and If I try to double click on they, Windows asks to me through which programs open them.
Put on a backup copy or restore point if you have one, what causes this, who knows but these do not help, registry cleaners, stopping services and uninstalling programs until you fully understand what happens when you do. There are some very neat programs here on MDL, and if it does not have a way to let you uninstall it, don't mess with it. People write neat programs, then move on, if program is not maintained.............
All the stuff that I've modded, was made when I installed Redstone 1 (last summer). This issue occurred suddenly and recently, less than a week and I have not touched anything.
None of this matter really except the above as a whole new Operating System which you should clean install (Best Too) will be out in 2 or 3 weeks, so...............
Been happening to me the last couple of days with image files, I always use Office 2010 picture manager as default, lately it's been asking me what I want to set as default whenever I open an image, so it's not setting it back to photos app, it's just losing all association