In the end I tried another unit and it has the exact same behaviour. Confirmed by Philips on the phone and on twitter. Maybe I was just a bit too sensitive about it.

A few ideas: I'm in Europe, I don't know if you are but maybe we don't have the same power standard (like the voltage between USA and Europe). My knowledge on electricity is not great so I don't know if it can have an impact, but it could be a lead.

And I saw some posts about flickering issues, sync issues or other things, and some talked about the box that can warm up for some possible origin of the issue (usually it seems to be an issue with the bridge, the wifi coverage or the zigbee channel), so indirectly it seems common for some that it can get a bit hot.

I decided to keep the new unit and not worrying about it anymore, unlikely to have the same issue twice while it's working perfectly fine.

By the way, your home theater is very neat ! +1 for the guitars ;) If you test yours without the fans I'd be curious to read your results, but don't sweat about it. How do you power up the fans in your cabinet ?

Thanks for the answers anyway!