Hey, aenoibanga! We don't have the disappearing badge notifications when you clear drop down/pop up notifications listed internally as a known issue, but after some good old fashioned Googling it seems like this is something a lot of folks are experiencing after updating to Oreo -- not just on Note8s, but other devices as well. After reviewing several other forums; I still haven't been able to determine if it's a deliberate behavior, though -- this kind of makes it seem so; but I don't know Samsung forums well enough to tell for sure! Badges with number disappearing while using android Oreo OS? | Samsung Support
Have you done any troubleshooting post-update, like a cache clear or even a Master Reset? I'm wondering if the issue still persists afterwards!
My note 8 did that missing notification bar too once in a while, it's not t mobile, it's Samsung, but since the may 13th Oreo resumed update no more issues, and best of all my batter is back and has life again, no more Oreo bugs. Works like it did back with version 7.1.1. But better and faster and the new features, too. C'mon note 9 August 2018. .... next iphone??? Uh huh possesses.