While Android 8.0 Oreo has not been made available widely for very long yet, it seems like a bug associated with the new platform has shown up. As per a user of the latest version of Google's mobile platform, the update has brought along an issue where the system is using up mobile data even when Wi-Fi has been turned on as well.
A Redditor who goes by the name 'Unusual_Sauce' has reported on the website that after updating to Android 8.0 Oreo, his/her mobile data usage received a huge spike despite being connected to the Wi-Fi, as pointed out in a report by 9To5Google. Some of the other users on the website have pointed out that the Android 8.0 Oreo update causes the "mobile data always active" setting under Developer Options to be enabled, as per the report. As this setting was earlier disabled by default, an issue might be occurring.
Due to this change in settings, the mobile data is effectively active even when the user's device is connected to a working Wi-Fi network. Users always have the option to disable the setting by heading to the Developer Options but the Redditor says that on being contacted, Google said that it is aware of the issue and is already working towards a fix for the same. For those who are not enjoying unlimited data plans, this bug can result in a hefty monthly bill and therefore needs to be fixed as soon as possible.