We have also been experiencing the random characters in parentheses prepended to the environment label. We also observed that the characters come from a deployment_identifier file located in our project's root directory.
I'm submitting
patch #20 →
which is similar to #9, but it keeps the environment_indicator.current_release state variable check. It only replaces the deployment_identifier fallback with a \Drupal::VERSION fallback.
As suggested by comment #9, patch #4 fixed list widths in our admin theme, but it ended up breaking some widths in our front-end theme, because the !important tag was overriding our front-end css list styling.
Submitting interdiff and patch #11, which moves the proposed styling fix to the chosen.claro.css file.