After a first contact with PearsonVue advising me to "just reschedule" as it was most likely due to a "technical issue" , their website showed :

"We are sorry, CompTIA Testing policy prohibits exam delivery in your location. To take CompTIA Testing exams, you may need to travel outside of Quebec. To choose an alternate location, please restart the exam selection process."

further probing of support services produced the following response

" We regret to inform you that we no longer offer testing in Quebec due to our inability to meet the Quebec French translation compliance requirements. These regulations mandate that the entire candidate experience, including exam content, website, and communications, be translated into French for Quebec residents.

Unfortunately, we cannot accommodate this requirement. Therefore, we have made the difficult decision to discontinue registrations for candidates in Quebec. "