Could it've been that you had an old 'unread msg' hidden in the depths of your inbox somewhere? I've had a couple of occasions where the 'Notification' flasher hasn't stopped once I've read all the msg's that've recently arrived, only to find one (or possibly two or more?) msg/s from MUCH earlier that hadn't been read.... :gaah:
I'm not sure how or when these msg's actually arrive, but I suspect there may have been some delay in them showing up in the inbox displayed on my device, despite them possibly having been hanging around as received & recorded against my profile/account inbox for a while (in one case, for 3 WEEKS! :shocked: ) Or maybe I read the top msg/s in a stack of them & then got side-tracked & went on to do other stuff, & just didn't notice that there was an outstanding notification on an unread msg.... :dontknow:
I really don't know, but these days if the 'Notification' doesn't turn off as soon as I've read to obviously new msg's, I go looking for something I've missed back a few days... or weeks! Might be worth a shot for you too! :thumbup: