Yes, rolling back is easy. Go here:
https://pgaskin.net/KoboStuff/kobofirmware.html
and download the firmware file for your device. Copy KoboRoot.tgz to the .Kobo folder and then eject to perform a manual update to the firmware version of your choice.
KEPUB uses 1 screen = 1 page, so it sounds like Kobo has either erroneously started treating EPUB files as KEPUB, or maybe Kobo is trying to unify the reading engines finally? What you're seeing is normal for KEPUB files but was not normal for EPUB, which should be using Adobe's synthetic page numbering system.