On 6th January, French Wikipedia started reporting the above error.
This is occurring predominately on Mozilla/5.0 (Windows NT 6.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.112 Safari/537.36 a browser which should have forEach support but doesn't have forEach support for NodeList API: forEach so I suspect that's to blame.
Given where this error is occurring I am pretty sure this relates to the sticky header deploy.
Possibly the line
userMenuStickyElementsWithIds.forEach( makeNodeTrackable );
Unable to replicate on browser stack using Windows 7 Chrome 49 due to an issue with browser stack date time.
Not able to replicate on browser stack using Windows 10/11 Chrome 49