I have a USG and am suffering the same issue. I have a few sites connected to my Controller on my Unraid and only after this last update has this Stun server port issue arrised.
I have the following ports open in my USG forwarded to the Unraid on both TCP and UDP
8443,8081,8880,27117,3478,8080
They are just listed out as above in the USG, are you saying I should swap this to
8443,8081,8880,27117,-p 3478:3478/udp,8443,8081,8080
Will that work?