Comment # 1 on bug 1221759 from Franck Bui

(In reply to Andreas Schwab from comment #0)
> [   80s] Mar 20 13:12:20 localhost systemd[1]: Starting Switch Root...
> [   80s] Mar 20 13:12:21 localhost @ystemctl[383]: Failed to switch root:
> Specified switch root path '/sysroot' does not seem to be an OS tree.
> os-release file is missing.

Dominique fixed a similar issue recently:
https://github.com/openSUSE/obs-build/commit/c295ac72c80dc1f4107c5c1ef703061b7b080869

The fix has probably not reached tumbleweed yet.

Dominique, do you confirm ?