It's by no means a common issue but I've had customers come through advising us of a similar fault. It's generally as a result of the Fetch set top box overheating. Does the Fetch unit ever become unusually hot? It's a good idea to ensure that the Fetch set top box is positioned in a well ventilated area. We'd first suggest trying a factory reset. You can find the instructions here → https://yescrowd.optus.com.au/t5/TV-Entertainment-Knowledge-Base/Fetch-TV-Hard-Reset/ta-p/133701.
It's important to note that any saved/scheduled recordings will be lost in the process.
If you've tried a reset and you're still experiencing the same issue, send us a PM with your account details. We'll need your full name, DOB and account number. We can look into organising a warranty replacement for you.