I now think this problem might not be due to Wireless Update itself, but some wider change in the 20200620 update. This is because I have seen increased notifications from three other apps, which I'm sure weren't happening prior to this update. In particular, these were Tor Browser, Handy News Reader, and Etar.
The behaviour is similar, in that a notification from these apps appears for a couple of seconds then disappears, with nothing of substance in the notification itself. In the case of Tor Browser, the notification icon is the exact same plain circle that Wireless Update shows (the o