The Samsung TV remote worked perfectly until the SONOS ARC was installed, hence not a TV issue. In fact last night I unplugged everything (power and HDMI) cables. The TV was turned on without the ARC soundbar connected and the Samsung TV remote totally worked. Then as soon as I connected the SONOS soundbar I lost the capability to change channels, the TV remote control can still change the volume though on the soundbar
I am personally stumped at to why attaching any soundbar to any TV would stop its remote changing the TV channels, so you are perhaps best to speak with both Samsung and Sonos Support Staff and see if they can assist you, rather than posting here to the Sonos ‘user’ community.
To help get you started, it maybe best for you to go onto reproduce the issue and submit a Sonos system diagnostic report from within the Sonos App, note it’s reference and then contact/chat with Sonos Support Staff via this LINK and see what the Staff can perhaps suggest to resolve the matter.