Occurred when tested https://github.com/jenkinsci/jenkins/pull/5067
Also occurring on 2.267, 2.260, 2.250, 2.222, 2.190, 2.170, 2.150, I am too late to the party :/
Working fine on Firefox.
Seems due to the water-mark icon in background. If changing "body .plugin-setup-wizard .modal-body .water-mark" font-size to anything different than 392px, I got the scroll disappearing. I imagine it's due to some JS code playing with style dynamically.