Why does my website page jump or shift visually when it first loads?

Visually shifting pages (Cumulative Layout Shift) happen when your theme fails to define explicit width and height attributes for images, ad containers, or dynamic banners, forcing the browser to recalculate the layout as elements load asynchronously.

“This tends to boil down to images and banners loading without explicit dimensions, so the browser keeps shifting things around as they load. I’ll lock in the right sizing within 24 hours for $99.”
— Jeff Bollettino, Managing Director, Ignite Conversions