In the Main Menu of your receiver/processor, navigate to the Setup Menu and Control Setup. Turn Off all CEC / ARC controls except CEC/LAN/BluOS in Standby-leave set to ON.
ARC and CEC are not clearly defined standards and as such, every manufacturer handles them a little differently. This often leads to unpredictable behavior as each manufacturer interprets the guidelines to optimize within their brand ecosystem. Changing one HDMI device in the system can make a once working installation no longer operate correctly with ARC/CEC. This is a very common issue throughout the industry across all manufacturers.
To insure flawless operation, an optical cable from the TV to the receiver is strongly suggested for TV audio. IR repeater kits and multifunction remotes such as Universal Remote, or ProControl will always be much more reliable than CEC. For large systems, full blown automation platforms like Control 4 and RTI may be considered.
We will keep publishing firmware updates to maximize compatibility, however the options above will always provide a better user experience. Some good news is the newly ratified HDMI 2.1 standard aims to improve these ARC/CEC issues in the future.