Missing data fom chat page

Facebook was fine last night but this morning it's a mess. Symptoms:

The "Cover Photo" at the top of each page is fine, as is the column of subjects at the left of the page. The messages in the center of the screen are not there but four of them always appear as blank white boxes. The message contents simply won't load. They will, however, load if I change the page URL from a www to an m-dot (m., or mobile) page. This occurs on all my computers, both Wi-Fi and ethernet connected, and only on Facebook.

I've tried rebooting my Wi-Fi connected laptops and my ethernet connected main desktop computer. Same problem.

I've tried rebooting my cable modem and my router. Same problem.

I've tried four different browsers - Chrome, Firefox, IE, Avast. Same problem on all of them.

I've tried two different ISPs - my main Comcast cable connection on my internal network and I tethered my Verizon phone to the laptop. Same problem.

I've discussed it with my IT specialist son and he can't find an answer.

I've tried everything I can think of with no result. Do any of you have any ideas? HELP! PLEASE!