I have tested 522, 521, 446. All the same @ 1440p Gigapixel appears to not apply its magic. I have even scaled to 1080p and then scaled (with same version) to 1440p and the result is indistinguishable.
I have recently bought a £600 1440p monitor which has a game & sRGB mode (my old monitor died while I was out of town). I have the exact crops (actually I have found that cropping does degrade quality itself, but that is before the cropping tool inside gigapixel came along, you need a fine rotation tool too), I have got 27 iterations testing cpu alone ect over 3 different versions.
I don’t feel like upscaling at all now because its such an obvious flaw and there is no workaround (except upscaling to 1080 then to 1440 but I simply refuse!).
There is a directory C:\Users\myusername\AppData\Local\Topaz Labs LLC which is common to all the latest versions. I completely uninstalled v 522 & v 521 before trying v 446, which showed the same quirk and it did not use that folder (I’m sure because its completely missing after uninstalling with revouninstaller).
The silver lining is that I am in the process of scanning right now… Hope you can address this in a future version.