Here's the list of what I'm using first, as I don't really know where the issue is...
I haven't done any updates recently (though maybe Windows has snuck some in)
So, couple of weeks ago when I last installed a packaged UWP app, all working fine. Today (so bug has appeared in last couple of weeks) when I go to install my latest package the installer says "you already have a newer version installed - click launch". Yeah, it works if I click on "launch", but that's all. i.e. i doesn't appear in the start menu, nor can I find it in any of my Program Files folders, nor does it show up in "uninstall a program". i.e. not a very good user experience when they have to launch it from the installer, and can't uninstall it.
I still had the package from a few weeks ago, so decided to try that for diagnostics (see if that still worked as expected. i.e. the program appears in the start menu). Got the same message about a newer version, and NO, it DIDN'T install at all. When I launch it I'm still getting the newer version (just like the message says). So now I also have a non-uninstallable program (which as far as one can see isn't even installed to begin with, but does run when you click on "launch").
Anyone experienced this? I suspect the issue is in Win10, but don't really know what to look at to try and fix it. May also be an issue with VS creating the package (which has corrupted something and now the old package doesn't work either).