Android notification dots appearing on random apps
As of now, this seems to be a bug and only appearing in OnePlus phones post the latest Oreo 8.0.0 update. It is unclear what they denote though.

Restarting the phone solves the problem temporarily. It will be safe to assume that a fix could come out in the next patch from OnePlus.

As @beeshyams discovered, this has been reported few times on the forums