Hi,
Could you share example of the log where this happens? Yes, there are some supernetting guidbedit things that changed in R80, compared to before in R77. There is also file on mgmt server called crypt.def for excluding certain IP ranges, but does not sound you even have that configured. Is it only one tunnel with this issue or multiple? If its one, you can simply reset it via vpn tu command on gateway, but if its multiple, sounds like it could be global issue. Happy to do remote session and see if I can help you fix it.
Andy