The git tool chooser will use locally cached copies of git repositories to estimate repository size. However, the cache lookup uses the repository URL as the cache lookup key. Git repositories on all major providers can be accessed from multiple URLs where the different URLs represent the same repository.
For example, https://github.com/jenkinsci/git-plugin and https://github.com/jenkinsci/git-plugin.git are the same repository but cache lookup by the repository URL will find at most one of those two.
Should extend the repository cache lookup process to better use the cached copies.