To aid in TCP hole-punching, the discovery server now processes more port information about remote peers. In reverse-proxy setups the discovery server can’t normally see the client’s connection port. In order to support such setups, the discovery server now interprets a custom reverse proxy header “X-Client-Port”. See the docs and the corresponding PR.
Note: These changes were gathered by comparing 1.7.1 and 1.8.0. Since the discovery & relay servers only see irregular releases, there may be more (older) changes involved that I overlooked.
Especially this part is a bummer though. One has to to hope for everybody to always have an issue for a change. Makes sense, but leaves open the possibility of code changes without according changelog entrys.