We’ve had this same problem with a couple of customers on Comcast in Florida the past week. We have customers all over the nation so I’m pretty sure it was related to their ISP specifically.
To quote a Bubble engineer from an old thread on this forum about a similar issue:
Odds are pretty strong that if these affected users change the DNS server they’re using, they’ll be able to access your site. This can be done on their router or on their computer. Please note that some ISPs block changing the DNS server as a security measure, so your users may need to contact their ISP for assistance with this.