Samsung S9 on Android 9.
Can't reproduce the issue on my other testing device (Nexus 5X on Android 7.1). Also tried on emulators with no luck.
@malinajirka confirmed that he was not able to reproduce this exact issue on his devices (Emulator + Pixel 3 Android 9).
The Uploading notification to be correctly cleared if I stop the Media Uploading by tapping on the media and selecting "Stop Uploading".
The network connection is correctly stopped, but the notification is still there in the notifications center, the progress indicator is of course stuck at the current position, and a new Upload failed notification is added to the stack.

See also Scenario 3 here.
I also noticed that sometimes weird things happen with media notifications.


Tested on current develop - d3c89dd7d4dcd3d138bc544642b3ace38cb2a96a
cc @mzorz
@marecar3
I've investigated this a bit further with images, and I see uploading notifications reporting wrong info when adding images to the editor and there are errors uploading them.
EX:


And then the app is stuck in the current state with notifications.
Note
In another test of mine I tapped retry in the editor and ended up in the following notification:

Scenario no. 3
https://cloudup.com/ccVRBOLfH28
I tried testing this a few times using WPAndroid alpha-170 on Pixel 3 Android 9 but I was unable to see any notifications in the system NC (41s). I tried checking notifications settings for the app itself and all looked well (screenshot).
I was able to see this happen today while testing with WPAndroid alpha-171 on Pixel 3 Android 9 with these steps:

Note: this notice seems like it should go away but it has been stuck there for quite a while after coming back from going offline in the middle of an image upload.
@malinajirka would you mind giving this one another go to see if you are still unable to replicate the problem in testing?
I think this PR might solve the issue. I have been testing it on my Pixel 3 a few days ago and I never ended up with a stuck notification.
@designsimply I'd suggest closing this issue until someone encounters it again. I tried to reproduce it today without success. I still hope it got fixed in #9956.
👍closing per the recommendation (and the hope it was fixed in #9956 🙂) with an ask to re-open if it comes up again.