I have the exact same issue with AT 8.1.6 and Cubase 9.5.30 when using DOP. Pitch changes are not applied after closing the DOP window.
BY the way, I dont get the question about creating a new version (as indicated in the previous post).
I think it did work for me in Cubase 9 at some point (see Process Plugin and Autotune 8.1 really really slow - Nuendo - Steinberg Forums), but am now not completely sure anymore.
It seems this issue was already present a year ago: Cubase 9.5 - Antares Autotune 8 - Not processing Audio clips - #2 by maartenl945 - Cubase - Steinberg Forums
Hope it gets fixed soon …
Regards,
Maarten