Hi Nigel, thanks for the testing. I thought I was going crazy for a while!
I managed to get it working although I have no idea why my original placement of the map marker won't work.
Your code:
The map marker was put directly between the <wpv-loop>......</wpv-loop> tags. Which works.
My code:
The map marker was in the 'Loop Items In....' box which in my head does exactly what you did above: it places the code in between the loop tags.
Well I moved the markers to the top and now it works.
The logins are still active if you want to have a look but I am happy with the workaround.