Some users no audio/video on, but can text chat, Rest of users fine

This is an utterly strange issue, and regular troubleshooting techniques have not resolved. So hopefully folks here can help us figure this critical issue out.

We have been using for about 1.5 years.
(We’re working on setting up our own jitsi server now that we’re using it regularly, but that is still a work in progress).
We regularly have anywhere from 1 to 7 people in there, several times a week.
Last week we had two new people join our volunteer group. With 2-3 others connected, and ourselves, we could all hear and see each other, text chat, desktop/application/window share, youtube stream, etc.
However, these 2 new people joined, and they could not hear or see us, nor could we hear or see them. Though we could see their avatar and we could text chat with each other. That was Thursday last week between 6-8 pm.
Today, Monday, from 7 to 10 pm, we had a different group of 2 people plus ourselves, and then these same 2 people tried again to join us.
They had the exact same problem. We had them try a different room on the server, but still didn’t work.
Both days we had them try both Chrome and Firefox. Same result.
We had both of them install the Jitsi app on their Android smartphone and try connecting over their wifi, and same result with no video/audio, and text chat only.
We had them switch to their cellphone providers bandwidth rather than their wifi (to rule out his network), and still same result on our end.
Putting them on s separate room, with just N (us), user 1 (B), and user 2 (T).
With B on cell phone and T on PC. B and C could see each other, but still not see us. B could hear T but not us. We could not hear or see either B or C. We switched from our Comcast cable network to our backup DSL network, and still had the same results.
B & C can hear and see each other, but cannot see or hear N. N cannot hear B&C.
We’re still trying every combination we can think of to get this resolved. Would really appreciate any additional suggestions.
Now with N on Centurylink DSL, B and T on their wifi, B & T can hear and see each other but not N.
We tried with a third network on our end, the Verizon Mifi. Still same result.
Note these two users, B & T, so far have never been able to see/hear audio/video with us, just each other. They have tried this past Thursday for several hours, and today for several hours.
Please, any help you can offer?

Addendum. One user is in Missouri. The other in Oklahoma. We are in Washington (Spokane).

Addendum: User N on cellphone, User T on cellphone, and User B on cellphone. B & C can see and hear each other, but N cannot see or hear B or C, and they cannot see N. All can text chat. N can connect via phone to our chatroom no problem. We’re stumped.

We have this issue also. The chatroom was The user who couldn’t participate last Thursday was in Missouri. Those who could were in Michigan, Arizona, DC, Massachusettes, Missouri. Tonight we had the issue again. The users in Arizona could participate; the user in Texas dropped out every time another person from AZ joined.

This Thursday, we had 7 people join us, including the 2 from last Thursday, and the other 2 from Sunday. This time it worked for the most part, though people needed to keep refreshing their browsers about every 10 to 15 minutes because audio or video would start glitching/stopping.
We’ll see how it goes this Monday and Thursday.