Why SRMA did not work for you
Stop Resetting My Apps did not work for you? Let's check that out.
First of all let me tell you why does Windows 10 reset the file associations. It all lies in one registry key: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts. This key is where Windows saves user preferences for file associations. Microsoft does not want applications to modify anything under this key, but not all of them respect that.
You see, Microsoft does not want applications to override the user's choice about file associations. And we could not agree more, right? But some applications want to forcefully be the default applications for certain file types and change some subkeys of the FileExts key to achieve that purpose.
With Windows 10, Microsoft started adding a hash value to each of the subkeys, which is associated with the last time the key was modified, so they can detect unauthorized changes to the subkeys. Whenever a change is detected, that file type's association is reset.
Also, some applications tamper with the permissions (ACL entries) of those registry keys, which also changes their modification time and date, making the hash value invalid, and causing the file associations to be reset.
Stop Resetting My Apps does not work in those cases because it is a hardcoded Windows feature. You really have to make those applications stop messing with the aforementioned registry keys. Some applications have an option like Check for file associations at startup. Try turning that off or otherwise just get rid of those applications.
Now that you know why SRMA did not work for you, lets try that again and find that annoying application that is making Windows reset your default apps!