beveltd on "importing xml to page can't be found"

Hi all,

I'm having a massive issue with wordpress, I don't know if the issue is a server issue or whether it's wordpress 4.5.2 but the situation is when trying to import posts, pages etc I get through step one assigning users once I click to continue with the import it seems as though it's importing but goes to a 404 page instead.

There are no plugins installed except for wordpress importer, the xml is only 653kb in size and there is no theme but the standard installed.

I already have my hosting company checking for server issues that may cause this issue, I've also read other posts (all quite dated) and they believe its something to do with nonce. I haven't got the faintest clue as to why this is happening or how to fix it...

In all my years of using wordpress I've never experienced this issue, can someone please advise of any ways to deal with this?

thank you kindly in advance