Ah I see. Thanks for clarifying that. The in-game changelog only seems to show the changes up to the installed version. I always check changelogs before updating mods.
It looks like the web portal is pulling the changelog from the highest version of your mod. In this case, it is currently pulling the changelog out of your 2.7.0 upload, therefore none of the changes for the 2.0 branch after you split them into two branches.
If that's how the web portal works, the only way the portal would show all changes for all version is if you embed a unified changelog that included all versions of the mod, including branches. That might not make the most sense for forks, and it could result in more confusion rather than clarity. (I'll also grant I'm probably one of the few wierdos that bother to check before installing!)
Good to know this is the limitation. Thanks!