Hello,
"The only thing I can see that could be causing the issue is all the offending payments have non UK keyboard strokes i.e. (Frysjøenden) in either the name or address, could the be the issue? and if so how do I cure this?"
Unfortunatelly no, this can't be able to leads to an notification issue.
For the other points, you have to understand that when we ask you some points to check, or ask for some configuration elements, we are expecting to get precise answer, otherwise help you will be difficult...
For the payment log :
see this tutorial
For
IPN history in your PayPal merchant account, did you as Nicolas told you, have some clues ?
Did you try to get some help
from Paypal support (to be sure that the issue is "HikaShop side") ?
Did you process some test with
Denmark address ?
Awaiting clear answer to theses points.
Regards