I get more Fork problems than average, plus my fork hurts my hands on the rough stuff. Could a Riser Steam be causing this ? The bike originally came with a 70mm flat stem and I thought that because the Bike’s original design was not designed to work with a Riser Stem, that maybe this could be causing the problems ?

No, cant see how it makes any difference to the fork. just in the same way using a higher rise bar wouldn’t, will feel different for you but not your fork.

Fork hurting your hands on rough stuff could mean too much air, too much compression damping, not serviced recently so increased stiction etc last thing I would be blaming is the stem

Jeremy Corbyn uses a riser stem. I don’t think that is the cause of his problems but it doesn’t do him any favours.