In github you can change the default branch to another branch.
You can also rename branches.
If you do this with the main branch, the addons will still be loaded from default branch.
Example:
main branch for development
release branch for releases
The github url contains no branch information
The default branch in git is release.
If you open this url in the browser, the branch is release
The addon store will load the addon from the development branch named main.
Workaround
Rename the branches to dev and main.
However, this can easily be fixed by reading the default branch from github:
(Make a call to /repos/:owner/:repo and read the default_branch property value).
Should this be fixed?