I've got a 6 month old hope pro 2 on my Whyte 905, its gained a bit of play, only a couple of mm at the rim but its irritating!
Any thoughts on what it could be?

uh, you need new bearings!

Yep,new bearings,5 in total.Just done mine due to having the same issues as you.

Depends what you mean by wobble – if the rim rocks when you hold it and twist, then bearings as suggested. If the rim moves as the wheel spins, then it's out of true and needs re-trueing

FIVE ?? Most Hope rears have 2 main bearings that cause the wobble and 2 more in the freehub that usually wear slower…

It will be unlikely that the freehub bearings are gone, probably be the main bearings. I found my non drive side went first for some reason.