We are aware of the issue happening in the 3rd beta of iOS 26 (we have an active thread in Discord). Can you confirm that you are in fact using the developer beta for ios26?
Unfortunately, until betas are more stable we don’t have plans to dedicate resources on a fix.
I’m having similar issues in the public beta of macOS Tahoe. The page preview shows all of the correct pages in a PDF, but when I actually try to flip through it in fullscreen, I’m only seeing a handful of pages that continually repeat themselves.
edit: I tried the public Testflight beta (3.8.0) and the issue appears to be resolved in the public beta of macOS Tahoe. Thanks!
edit edit: Running into an issue in fullscreen mode of the Testflight beta (3.8.0) where I get a bit of flickering at the very top of the screen, where the menu bar appears if I move the mouse icon to the top of the screen. Too distracting to use this way, but I assume this issue will be addressed in the final release.