My new-ish XTR freehub skips occasionally, not a huge amount, but definitely more than the deore on my other bike.

I'd attempt to go for a warranty but it doesn't do it predictably or frequently enough to demonstrate it to shop staff.

Is this a common issue, are they (easily) serviced?

Madison warranty are very good, I've never seen a claim on anything XTR rejected. I suggest it wouldn't be a huge issue if you couldn't demonstrate it to shop staff. Dismantling it may show the problem anyway.

What exactly is it doing? Presumably you've not changed your chain on an old cassette or anything?

Its an all new drivetrain. Initially I hadn't changed the big ring and blamed that, then i replaced the big ring and it still does it.

Once a ride (if that) isn't very much tbh, but i didn't buy XTR for it to perform worse than deore…

Its more likely to skip if i change pressure on the pedals. Just pushing really hard doesn't cause it. Makes me thing the pawls are just a little bit sluggish.

I gave the bike a really good clean a while ago, and although i didn't consciously aim any degreaser/water at the freehub area, i'm wondering if some got past the seals anyway, pretty sure it didn't do it before I cleaned the bike.

Annoying vague problem all round really!

New chain too?

I had an XTR freehub replaced on warranty not long ago. It had started by skipping and progressed to not catching at all. It was no bother to replace apart from finding a 14mm allen key needed to get them on and off.

Yep, replaced the lot before the merida marathon at selkirk, except for the big chainring. Then replaced the big chainring soon after.

Haven't checked the chain wear as I haven't used the bike much, but i think its safe to assume the chain isn't worn, and the chainrings/cassette all match the chain. Have fitted a singlespeed drivetrain for the winter which hasn't displayed the same symptoms, but i've been deliberately taking it easy on the new setup.

Might research stipping the freehub and regreasing, problem is guessing the right weight of grease…

Will look into a replacement, but I doubt they're cheap!

I'd just use the Shimano grease. You can't really strip the Shimano freehubs come to think of it, so you may be best just sending it back.