Not sure what you're going on about. I tried replicating what you describe, but `git switch` keeps working just fine.

    ~/tmp/foo git init repo1
    Initialized empty Git repository in /home/user/tmp/foo/repo1/.git/
    ~/tmp/foo cd repo1
    tmp/foo/repo1 ‹master› echo hi > hi
    tmp/foo/repo1 ‹master› git add hi
    tmp/foo/repo1 ‹master*› git commit -m hi
    [master (root-commit) d0cf572] hi
    1 file changed, 1 insertion(+)
    create mode 100644 hi
    tmp/foo/repo1 ‹master› cd ..
    ~/tmp/foo git clone repo1 repo2
    Cloning into 'repo2'...
    done.
    ~/tmp/foo cd repo1
    tmp/foo/repo1 ‹master› echo hi2 > hi 
    tmp/foo/repo1 ‹master*› git add hi
    tmp/foo/repo1 ‹master*› git commit -m hi2
    [master 3a82bdc] hi2
    1 file changed, 1 insertion(+), 1 deletion(-)
    tmp/foo/repo1 ‹master› git checkout -b someotherbranch
    Switched to a new branch 'someotherbranch'
    tmp/foo/repo1 ‹someotherbranch› git 
    tmp/foo/repo1 ‹someotherbranch› echo otherchange > otherchange
    tmp/foo/repo1 ‹someotherbranch› git add otherchange 
    tmp/foo/repo1 ‹someotherbranch*› git commit -m "otherchange"
    [someotherbranch 99ec880] otherchange
    1 file changed, 1 insertion(+)
    create mode 100644 otherchange
    tmp/foo/repo1 ‹someotherbranch› cd ../repo2
    tmp/foo/repo2 ‹master› git remote add upstream ../repo1 
    tmp/foo/repo2 ‹master› git fetch upstream
    remote: Enumerating objects: 8, done.
    remote: Counting objects: 100% (8/8), done.
    remote: Compressing objects: 100% (3/3), done.
    remote: Total 6 (delta 0), reused 0 (delta 0), pack-reused 0
    Unpacking objects: 100% (6/6), 448 bytes | 448.00 KiB/s, done.
    From ../repo1
    * [new branch]      master          -> upstream/master
    * [new branch]      someotherbranch -> upstream/someotherbranch
    tmp/foo/repo2 ‹master› git checkout master
    Already on 'master'
    Your branch is up to date with 'origin/master'.
    tmp/foo/repo2 ‹master› git rebase upstream/master
    Successfully rebased and updated refs/heads/master.
    tmp/foo/repo2 ‹master› git switch someotherbranch
    branch 'someotherbranch' set up to track 'upstream/someotherbranch'.
    Switched to a new branch 'someotherbranch'