So it's definitely something being blocked - I set up my FB account to send notifications to a different email address, one on a server I have my website on, completely different domain - and it's working fine now. So FB was trying to send notifications to my Cox email address, and they weren't going through (wasn't downloading them - I use Thunderbird for my main email client on my PC).
So that says to me that FB either stopped sending them to the cox.net (or ph.cox.net, or ph.ph.cox.net) (sub)domain - or they were being filtered in some manner - and it was likely because of the fire/arson, and bounced emails triggering the filtering (or non-sending, most likely).
On a different note, the reason I couldn't get to the admin panel on my hosting service was because they had changed things to disallow going to the page from non-whitelisted IP addresses - it had nothing to do with anything else. It was a security precaution they were taking, but never sent out a notice about. Instead, I guess they figured it was easier to wait for people to complain to support staff about the issue, and have them whitelist the IP address (which is probably true - most of their clients likely don't do their own admin, but farm it out to an agency or other webdev service).
But how many other people out there aren't getting FB notifications because cox.net (etc) is blocked? I dunno. Maybe I'm one of a very few who uses a browser and thunderbird for the majority of my internet (and most people use the FB app on their phone or whatnot)?
I wonder if this will ever be resolved? In my case, it doesn't really matter now - I've resolved it myself for now. But it shouldn't have to be this way, and most people won't have that option.