Riot isn't an alternative to Jitsi so much as a complement to it. Matrix is for text chat, and Riot uses Jitsi for calls; while you can embed a Jitsi client into Riot rooms, and it auto-shares the URL, AFAIK group calls are not E2EE even if the room is.
One-on-one calls through Riot _are_ encrypted, but only if made in a one-on-one direct chat.
We were facing the exact same issue this morning with our own .ml domain - one of our engineers was accessing it no problem from 1.1.1.1 but another couldn't see it with 8.8.8.8. After a couple hours of trying to figure it out we figured it was just some configuration we botched, somehow, with Google but _Google having an outage_ makes a lot more sense.
One-on-one calls through Riot _are_ encrypted, but only if made in a one-on-one direct chat.