I thought I'd share my experiences. Having used the Soundbar 500 for a few months and having periodic outages with the HDMI ARC TV sound, I gave up and switched to Optical. The app has a setting to "Auto Wake on Sound". Its a bit of a pain needing both remotes, but far less than never knowing when a reset of the TV was needed.
Anyone still complaining about this should switch it out and forget HDMI.
My own view is that Soundbar and TV manufacturers need to get their experts in the same room and ensure better interoperability. A feature should not be sold without it working and being fit-for-purpose.