what does it mean "audio/video source is invalid"

Watch video on AMC.com using Chrome on IPAD PRO 2020 and intermittently after commercial break screen goes black with the alert "audio/video source is invalid" Clicking on Close nothing happens. The windo close X appear for a few seconds. If you hid refresh the video restarts from the beginnnig and I have to move the progress bar to where i left off then it happens again not necessarily the next break might be a later break. Any ideas. With Safari it is worse itgo to completly black screen after each commercial break and can't get out of ot except restart Safari and ir starts from the beginning of the episode.