I actually posted a post about this before. And from a conversation I had with Sonos support they say this is normal. Um... I thought this was a bug but they said this is normal.

Of course, this can be considered normal in terms of marketing strategies. This is because it will encourage people to purchase separate subs. If LFE from surround sound and overhead channels is managed through a woofer built into the soundbar, it is good for consumers but not for sellers because it creates tremendous progress in the Bass experience.

When Sonos Beam Gen 2 is used alone, the LFE signals generated from the surround and overhead channels are not processed by the woofer embedded in the beam. Only the LFE generated from the L,C,R channels is processed by the woofer embedded in the bar. Therefore, when LFE occurs on the surround and overhead channels, an empty can is heard rather than a grand bass.

On the other hand, when the rear speakers are used together, such as Sonos Beam Gen 2 and Sonos Era 100, the LFE generated in the L, C, R channels are managed by the woofer built into the soundbar, and the LFE generated in the surround channel is delivered to the woofer built into the rear speaker, which greatly improves the bass experience of the surround channel. However, the LFE generated by the overhead channel is still not handled by the woofer built into the beam or the rear speaker.

What if a sub is added to this? It will manage the LFE signals on all channels, including the sound generated from the overhead channels.

Therefore, it is designed to gradually improve the Bass experience as the home theater configuration expands.