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.
The main Syncthing changelog covers those as well, it’s just we don’t publish new binaries for them with every Syncthing release if they didn’t change. (Which is the norm.)
The changelog itself consists of resolved GitHub issues for the release in question. If something changed but there wasn’t an issue for it it doesn’t get into the changelog.
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.