Just adding my two cents as a customer since 2017, and lurker since 2015, who has purchased a number of UHF shirts.
I alas agree with others on the UHFs that the issue is obvious and fundamental: they're ugly. I find the shades of green and blue really odd - neither dark, nor light.
It might be a different story with the nicer shade of (emerald?) green that was used on the 203/206. I should add that I would snap up a 264 emerald green/black ombre in a heartbeat.
Could an issue be the lack of pattern symmetry at the front? Not all previous collections have been fully symmetrical, but these stand out to me.
It is the main reason I opted against the 335. Great idea and nice colours but lacking in final execution. I hope slow 335 sales do not dissuade you from making more herringbone UHFs - there's so much potential there.
With the ombre shirts, 180, 203/206s, and 230, the patterns line up better with shirt when it is buttoned up. These are much more appealing designs, in my view.
The front of the garment is the customers' first impression. The 336/342 and how the white doubles up clumsily at the front, it is a surprising lack of attention to detail. I concede that I am fussy, and usually opt for less loud designs. However, IH also prides itself on the details.
On non-UHF garments, and looking at the outlet, I think you could reduce your outerwear offering, with more focus on your own icons.
Outside of the denim jackets (including rider's jacket), no light cotton piece of IH outerwear has ever done it for me. But I could be wrong, I don't have access to the sales figures, of course.
I also snapped up a IHW-11 at full price and was surprised to see it end up in the outlet. So what do I know. No regrets on that one, by the way. I hope that my comments are read as constructive as I intended. Thank you.