Happening to me too. one of my players can get in just fine, but i and another player got 503 errors on the main roll20 page, and when we tried to load our game, it's stuck on the black "Loading..." message and never going anywhere.
I am also having the same issue when I start the online playing. It will occur after a new purchase of Linksys WRT1900AC AC1900 Dual-Band Wi-Fi Router. Always I am getting no internet connection. but when I try to use other apps so it was running. I already contact my Linksys router support executive and he said router will ok. So why I am getting this when I load the game.