Reported in the dark-theme plugin ( https://github.com/jenkinsci/dark-theme-plugin/issues/79 ) by timja and confirmed by fqueiruga using Bootstrap in the admin panel is causing various rendering issue (Bootstrap causes the specific pages where it's used to have a different font and basic theme than the rest of the UI.)

AFAICS Bootstrap is used for the alert boxes used in the admin page (success, info, warning, error) and Bootstrap was imported to match what was done in the "Manage Jenkins" screen for monitors

It seems possible to do without it ... let's try