If AccuBattery and other background apps are getting killed by your OnePlus device after the recent Oreo update, AccuBattery's history page will be split up into many separate pieces. Usually adding us to the exceptions list of task killer apps and battery saving features in the system settings will prevent this, but some devices can be extremely aggressive in trying to manage power consumption. The workaround is to enable the lock symbol for AccuBattery in your phone's 'recent apps' list. This is a persistent setting that only needs to be done once. The downside is that this will also mean that you can't swipe the app away from the recent apps list.