This issue has been raised in the past. Are you able to confirm the make and model of the device you're using to stream Optus Sport with? The issue we've been advised of impacts customers using Apple TV to stream the live broadcast.
“This issue occurs for customers that are viewing via Apple TV – issue is being investigated by the vendors and a fix is in place until the next software update release."
If you're using a different device, please let us know and we'll raise with the issue with our TV & Content team.