It's not a bug, it's a feature.
Yours is an Oppo phone as well I assume?
Looking at the article I posted previously....
https://www.themobileindian.com/how...id-device-manager-on-android-smartphones-8957
Google recently announced a new service - Android Device Manager,
And with Color OS that Oppo devices use, it's showing the yellow "Device Manager is on" warning.
I'm pretty sure this is an issue that Oppo needs to fix with Color OS, possibly with an OTA update. Color OS is a heavily modified and customized version of Android, that's mainly used in and was originally intended for China, where there is no Google services basically. That's likely why I haven't seen it on an Oppo, and my new Huawei Mate 10 doesn't have this Android Device Manager either. I think this type of warning is specific to Oppo's Color OS, because if you root it, it will show a red "THIS DEVICE IS ROOTED" warning in the notification area.
I suspect this problem may also affect non-Chinese variant Vivo phones that use Funtouch OS, which is extremely similar to Color OS. Both Oppo and Vivo are really the same company, BBK.