Hi Diddly Doo
Just incase your problem isn't yet solved....... I had the same problem, tried everything & couldn't fathom it out.
Opened Microsoft Store > clicked on 'library' > at the top above the list of installed apps look for ' Apps ' 'Games ' ' Film&TV ' 'Included with Device' > across from there below where it says 'Get Updates' you should see 'sort & filter' click on it, it has a dropdown menu, untick 'show installed products only'. Then click on 'apps' 'games etc, they should all be there. Found this by accident & got all my owned apps back. The only problem is that I have to do it everytime I open the store, but they are still there. Hope this works for you.
Cheers.
Blimey has this bug been fixed yet?