I've got a 65" TCL Roku TV and a Denon AVR-S540BT receiver. I've had the receiver hooked up to the TV via ARC since May and it's worked perfectly until a Roku system update a couple weeks ago. Now it is VERY unlikely to send audio to the receiver when I first turn the TV on. It's set up for CEC which has also worked until the recent update. Most of the time the audio does not work even though the receiver turns on with the TV. The TV is trying to send audio somewhere (since there's no system audio from the built-in speakers) but I don't get any sound out of the receiver unless I go into the system menu and have it scan for CEC devices. Until I do that it reports that there aren't any CEC devices. It looks to me like the startup check for CEC is running before the HDMI handshake is complete.
Check out this Reddit thread for other people reporting the same/similar issues:
After following instructions above. I still have the same problem as the others above with my TV and DENON AVR 740 receiver. My TV Hinsense 65R6+
software 9.1.0. Serial number. YN00XH201447
jean in Ontario.