I am going to speak up for the AF parts i did mine including water pump all AF parts. have covered some 10k since and following this post have just done an inspection and all is well.
if all parts are running smoothly there must be some sort of alignment issue going on.
i hope you get things sorted soon and sorry i could not be more help 2012 Vogue 4.4 TDV8 - Current
2014 Navara V6 - Gone
2004 Vogue TD6 - Gone
Grand Cherokee - Gone
Discovery V8 (LPG) - Gone
Discovery TD5 - Gone

Lovely part of the world. At least you’re not going to get nagged at on the way
Maybe a break from your fatty will give you some fresh ideas

Jayk I also got mine from af and currently still okay having now covered about 200 miles 2016 4.4 diesel

I’ve never had an issue with AF parts in the past but this one pulley was definitely wobbling compared to the genuine one, getting it booked in to be sorted, 2012 Range Rover Westminster 4.4 TDV8
2006 Discovery 3 HSE 260k miles and still going strong with a new owner

Just got the car back from my local indi who hopefully has fixed the problem in time for my trip to the gaff in north wales, after stripping it all down again and checking everything they found the power steering pump pulley wasn’t running true, turns out the rear bolt had done a runner 😳 this caused the pulley to twist and this was the cause, all back together and so far running ok, fingers crossed it stays that way

Looks like I’ll be selling all the new parts I bought from AF for half price to try to recuperate some if the costs 2012 Range Rover Westminster 4.4 TDV8
2006 Discovery 3 HSE 260k miles and still going strong with a new owner

Pleased to here this has been fixed. Good that the indi got it in so quickly 2016 4.4 diesel

That fits with the belt being OK while idling but coming off on a short drive as the PS pump would only be under load when turning corners.

I think it'd be more to do with oscillating faster at higher revs, faster than the tensioner could deal with allowing the belt to jump sideways.