- Check whether you have a good internet connection
- Reload the browser (Ctrl-R or F5)
- Reduce bandwidth usage by turning off video
Here you can test the bandwidth; if everything is in the green zone, it should be fine.
If a firewall only allows TCP and no UDP packets through, this can cause delays or the transmission may not be lip-synced. UDP packets are transmitted more quickly over the internet, and if one fails to arrive it is ignored, which is barely noticeable with audio and video. With TCP, the receipt of every packet is acknowledged, which can lead to delays, also because a detour via a TURN server takes place.