Confirmed. my apologies it seems ti be a conflict with Air theme background. Jist tried a preview of just Discourse Search Banner with Chat plugin.
see below
Sorry for the incorrect duiagnosis… 
Taking a further look in the Air Theme the blue part of the background is blocked in that center column when scrolling the blue is just on the outer edges. When chat disabled the blue part of the background connects from left to right through the center.
vs
