A recent OTA update pushed out to Nokia 7 Plus users on the Android P Beta is apparently sending user devices back to Android Oreo. In a bizarre twist, the OTA is appearing as an update to the handset's Android Security Patch level, claiming to update that to June 2018. That's according to a slew of user complaints posted to the official support site for the HMD Global-built devices. Interestingly, the system reverting to Android 8.1 Oreo isn't at all the only problem being reported either. Issues range from complete phone failure via system freezes on bootup to a complete breakdown in versioning. Manually attempting to reapply the Beta package is said to fail because the newly installed package is a newer timestamp than the beta. That rules out sideloading but rolling back the update manually also doesn't seem to work for any users on the board.
As of this writing, a complete factory reset using the device's recovery menu seems to be the only viable option for those that are able to boot past the initial Nokia logo screen. That places the device back on Android 8.1 Oreo, requiring users to go through the entire setup again if they want to take part in testing Android P. It bears mention that even going the latter route will require a wait for a new version of the update due to the problem with the version numbers and timestamps as outlined above. Of course, that's not going to be anywhere near ideal for more tech-savvy users choosing taking part in the beta. However, it is far better than the circumstances surrounding a corrupted OS could have been and will at least eliminate some of the bigger problems being reported from the wayward update.
Since the issues are occurring on a beta program for the OS, users shouldn't be too surprised that any update associated with the firmware is breaking things. With that said, this goes a bit further than the usual problems with one or two force-closing applications. So it shouldn't take too long for the company to implement a fix. In the meantime, a moderator on the board has since responded with a promise to respond further with more details as they become available.