Archive not working in month view

I have been trying to solve this for months in the blog section “Archives by month” will not work.

the individual posts work so do the tags but when you go to Archives May2014 for example you just get a white page.

it does work in a different theme so i think it could be theme specific.

Any help would be great

this is the address

https://dolffanogfawr.co.uk/blog/