Response from Squarespace helpdesk ticket as of the 25th Jan
'I can confirm this is related to an issue with Bio Sites intermittently not loading on various networks. Our Engineering team is aware of this issue, and they’re currently working towards a fix.
We have been instructed by the Internet Service Providers and Cellular network providers to ask their customers to reach out to them directly. The issue is on the ISP end and we are not able to affect it on our end.
We’re unable to guarantee a follow-up or offer an ETA for resolution, but I can assure you that we’re working to have this resolved as soon as possible!'