My ONN. Roku TV loses the audio 'sometimes' when the sleep timer is used and the TV is turned on again. I immediately notice the audio sputters, goe in and out, until I restart the TV at which point it is fine. I notice there are topics where this happens with the ROKU device so it doesn't seem to be a fault with the TV.
Any suggestions on what to do other than rebooting my TV for however many more years I may have this TV? Bought during Black Friday 2019 along with my daughter who does not have this problem. She brought one for my granddaughter last week.
Have you tried contacting Onn support yet to inquire further? I'd suggest starting there to see what options or suggestions they can provide. Each Roku TV manufacturer provides direct support for their products running the Roku OS.