Very similar problem. Odd solution.
Logged in to UK store on a variety of devices, & some but not all the UK originated apps seemed to think I was still in the US store. I kept getting the 'wrong store' message when trying to update. Went back to all devices 5, 5s, 6s iPad 2 MB Pro and made sure all were set to uk. Tried changing to US and then back to UK. Various reboots. Made sure I wasn't logged into the cloud in a different ID. Swore a great deal which I did find helpful. Still I was getting same issue.
My solution, albeit defying logic, was to delete the app on each device, then go into App store (still the UK) and find each deleted app again. My intention was a clean reinstall of each offending app. What I found was that back in the bosom of the UK store, each 'deleted' app only gave me the option to update not install. Made no sense to me but I hit the update button out of exasperation and lo, it updated and the app popped up all nice and new and shiny on the desktop. No nasty 'your in the wrong store luv message' of old. This worked for the 5's, the 6 and the iPad.
If there's someone out there that can explain what I was doing wrong and how my 'solution' then solved the crisis I am all ears?
I still love Mac though like a true convert!