How interesting. For the want of something better to do I googled the string "agreement of the mayor on the basis of evidence" and got just the one hit - DTC:
http://dovertowncouncil.gov.uk/wp-content/uploads/2016/07/Full-Agenda-Ext-Full-Town-Council-03.08.16.pdf
So the sanction provision seems to have originated with the Finance and General Purposes Committee of 15 June 2016. I think I can understand that to vote on whether or not a councillor is refusing to take part in what-have-you is a misuse of democracy (shades of Lord of the Flies), but a binding 6 month suspension (committee membership) and indefinite suspension (external representation) imposed by one person and without appeal for an
apparent refusal does strike me as odd/unique.
Ironically, Councillor Wanstall was present on 29th June 2016. I wonder what he said yesterday.