11-30-2018 06:41 AM - edited 11-30-2018 06:44 AM
Since it seems you haven't actually performed the Oreo upgrade yet, I would first see if a cache wipe solves the current problems with Nougat, see if its in good running order, and only failing that do a hard reset before doing the Oreo upgrade - instructions for both are here (my earlier post on this forum):
A successful cache wipe should restore good working order on Nougat without affecting the current set up, hard reset is a last resort to "out of the box" status, losing everything you've put into the tablet so far. I'm not sure if a hard reset to Nougat will immediately restore the Oreo update - it may take some time to reconnect with Lenovo's databases.
My personal experience with the Oreo upgrade on Tab4 8 a couple of days ago was very good, none of my previous configuration or stored data were affected, and it's running well. Cautions that I'm not sure and haven't heard how well microSD "adoptable storage" (instead of ordinary "portable storage") formatting handles the upgrade, and be sure you have a full battery or hook up to a charger since running below 30% battery will stall the upgrade process.