"App is running" notification

[Android Central Question]

I must have ticked a box somewhere but ever since last night when I clear a certain app I get a notification that won't going away telling me "App is running" and prompts me to "more information or to stop the app".

I don't mind the app running in the background, in fact I want it to. However, the notification can't be cleared and it's got my OCD up in arms.

Any help is welcome.

Thank you.