When Windows sees change to the link to a pdf file association it will often try to reset it to edge but it does not always ensure it is restored correctly. It will happily try to keep all the old pdf historic associations even if they are no longer correct. thus you may see what looks like a valid old link but behind the scenes it links to a file that’s no longer there.
Assuming you have not changed the filename to not include “sumatra” at a command prompt you can try (beware each search may take some time)
reg query "HKCR\Local Settings\Software\Microsoft\Windows\Shell" /f "*Sumatra*" /s
and
reg query "HKCU\SOFTWARE\Classes\Local Settings\Software\Microsoft\Windows\shell" /f "*Sumatra*" /s
Ideally each should only return ONE same entry pair
but in my system I get 5 old pairs in each case and neither first or last is the default, that is found from
reg query HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf\UserChoice
that entry stores a hash value and if for whatever legitimate UserChoice reason the hash changes it may not function (damn MS multi-layered security blockers)
A related issue is shortcuts are not always reflected by the registry entries and the start tile can even point to a different location to the one it pinned previously to the taskbar
I find this most common when using the taskbar and context menus when changing between daily builds, so there I have used one common location workaround which is not the same as my default, because the alternative is to remove and replace the links each day I update.
The only way I know for ensuring the association is restored is to first ignore every existing link and do a totally fresh association which involves right click a pdf select “open with” and ignore any SumatraPDF icon keep taking last option until you “Look for another app on this PC” and select the desired current EXE most importantly with “always use” active
