Just need tightened up or is hub failing or something?

dont know cannot see it

Generally if the entire cassette moves as one its the free hub [ and it wobbles as one /you can feel /see play] – assuming its separate cogs type – and if the gaps are between the cogs its not tight enough / a spacer has broken [ unlikely]

tighten it and see what happens is the first move

if nothing its the free hub

Just started happening or newly fitted cassette?

Just found the same myself on a new DT350 hub. Turns out I hadn’t located the smallest cog against the splines properly, so the cassette wasn’t being fully tightened down

Weirdly, the same happened to me – DT Swiss hub too 😕

Axial play or radial play? Have you got the little 10spd washer/sim fitted? I installed a cassette once without the shim and the lock ring didn’t fully tighten up against the sprockets and the cassette rattled when ridden. Strangely it didn’t affect shifting so obviously a small amount of play.

Weirdly, the same happened to me – DT Swiss hub too

+1

I’ve got a rebranded Giant (DT Swiss) and this happens every other time if you don’t take care on the last cog.

Had an XTR cassette where the rivets that secured the individual gears to the spider started to fail resulting in visible play on individual rings.

Had to dump it, but as it was due a swap anyway, no tears were shed.

I’d recommending taking the cassette off for inspection of the rings and freehub body.