My q6 series Samsung has the same exact problem. It started immediately after I bought the TV. Samsung sent a technician to troubleshoot. He did a full reset and it worked temporarily. Now ARC and CEC stop working intermittently. Sometimes it'll work for a few days, sometime a few hours. I have to unplug it and plug it back in and it will work again temporarily. I have owned MANY Samsung tvs and never had a problem. This is unacceptable. I will never own another Samsung TV again. They do not stand by their product or their loyal customers.