px_eliezer_ The availability of servers on Ookla and other speedtest sites is always in flux.
Ookla regularly updates their servers hardware and OS, and takes those locations out of service during the activity. Usually (although a few locations are exceptions) the sites eventually return, but depending on the details of the maintenance (replace the rack servers (requires local hands assistence), or upgrade the OS (might be able to be done remotely if they have proper OOB facilities)) the time-frame can vary substantially. Back when the OS their servers were based on went EOS they upgraded a substantial percentage of their nationwide servers a few at a time over months.