Bearings all seem fine, running silky smooth on the bike. Issue is that there is play when the wheel is in the fork, but I can't feel any play when the wheel isn't in the fork

Causes a similar vibration to riding without sufficient spacers in the headset..

Thanks in advance

Tried another wheel in the fork? Does it also have movement? At least you know then if it's really the Pro3 or actually the fork's moving.

Tried another wheel, no vibration at all. Deffo the Pro3

some Pro IIs were known to have play with Maxle 20mm bol thrus, never seen an explanation other than the obvious (differences in tolerances) or any solution.

This a a road bike..thanks though.

I know this is a bit obvious and basic but have you tried a different quick release? Hope q/r don't have the best record.
It's one of the reasons I'll switch to 15mm bolt throughs on mtb in future.

Yup, tried a different quick release. Same issue. Hmmm

The bearings in my front pro3 weren't seated properly when I got them, caused some vibration, although out of the bike all ran smooth. A couple of clowts with a mallet and bearing tool sorted it in seconds…

If it's a Pro3 road hub try tightening the 2 part axle up, the 2 halves screw together and can sometimes come undone.

It is a Pro3 road yeah. I take it those will be the two allen key bolts at either end of the hub? If so I've already had those off to check the bearings along with a retighten.

thanks