Sorry to but in, but AFAIK
(see below) this is part of the specifications of the new 260/360 Sony projectors.
With 4k 50p and 60p only 8 bits can be used so you get banding. With 24/25/30p this should not occur.
The video processing boards of the 260/360 have a limit of 12,6Gb/s.
If you want full 18Gb/s you have to go to the 760 (laser projector).
What I heard was that full 18Gb/s data stream from input to panel output would be a very expensive videoboard upgrade setting the pricepoint of these projectors back to few k$ more.
Don't mix the HDMI chipset with the full videoprocessing board. The e-shift JVC's might have 18Gb/s hdmi chipset (costing only a few $ a piece) but they throw out half the data right away so their videoprocessing board can be made much cheaper. Don't know all the details though but that was what I heard.
Originally Posted by https://www.sony.nl/pro/product/projectors-homecinema/vpl-vw260es/specifications/#specifications
Video signal input
480/60p, 576/50p, 720/60p, 720/50p, 1080/60i, 1080/50i, 1080/60p, 1080/50p, 1080/24p, 3840 x 2160/24p, 3840 x 2160/25p, 3840 x 2160/30p, 3840 x 2160/50p*4, 3840 x 2160/60p*4, 4096 x 2160/24p, 4096 x 2160/25p, 4096 x 2160/30p, 4096 x 2160/50p*4, 4096 x 2160/60p*4
*4: YCbCr 4:2:0 / 8 bit