Ok, so what you call 'notification' seems to be in fact the application itself opening (you still didn't include any screenshot showing a notification so let's assume it's a vocabulary error)
could you
$ killall update-notifier
$ update-notifier --debug-updates
Ok, so what you call 'notification' seems to be in fact the application itself opening (you still didn't include any screenshot showing a notification so let's assume it's a vocabulary error)
could you
$ killall update-notifier
$ update-notifier --debug-updates
ANd copy the log there?