The game can sometimes appear to freeze. There could be several reasons for that:
1. The game is waiting for someone to play. Sometimes, people take longer to discard or call a tile. While the system waits for that player, it may seem the game is frozen. A message will indicate who you are waiting for, and since you are connected through audio/video, it might be good to ask the player verbally about their play. If they say they have played, then it's possible their move did not make it to the other players (perhaps due to some internet issues). In this case, the table leader can attempt to solve the problem, by invoking the "Fix frozen game" function in the gear menu. This will resend the tile to the person who missed it and they will get a chance to play again.
2. A player is disconnected. If someone loses their internet connection, a message will be shown. During that time play is stopped, and players should wait until the disconnected player returns. Most of the time, disconnects will be short and the game will resume automatically. If it does not, once the connection is restored, the table leader can invoke the "Fix frozen game" function in the gear menu. If the player is still disconnected after 1 minute, the table leader will be given the choice to wait longer or replace the disconnected player with a bot.
3. The device or browser locks up. Sometimes, devices or browsers experience lock-ups. This may happen if they run short on memory for instance. Unfortunately, there's not much you can do in this case, other than try to close apps to free memory. If that does not do the trick, close the browser tab (or the whole browser, maybe even the device in extreme cases) and relaunch the game.