Persistent eARC dropouts on Philips 75PML9506 + Sonos Arc (with surrounds/sub) + NVIDIA Shield — tried everything, need advice (HDfury? FeinTech?)

I’m hoping someone here has seen this before, because I’m running out of ideas. My Sonos setup has been rock-solid for almost two years, and suddenly the audio keeps switching from the Sonos Arc (with surrounds + Sub) back to the TV speakers, then back again. It happens on both YouTube and Plex, usually every 4–8 minutes but not on a fixed schedule.

My setup:

TV: Philips 75PML9506 (no firmware updates in over a year)

Sound: Sonos Arc + Sub + two rear surrounds, all wired via Ethernet (Wi-Fi tested too)

Player: NVIDIA Shield 2021 (no recent firmware updates)

Cabling: Recently replaced the HDMI eARC cable with a certified high-quality HDMI 2.1 48Gbps cable

All devices power-cycled, reseated, unplugged/reconnected in the SONOS-first sequence

What I’ve tried so far:

Completely removed all cables and re-installed the system in the order Sonos recommends (Arc first → TV eARC setup → add other devices)

Tested with only the Shield connected, then with only the Switch connected

Tested TV audio modes (Auto, PCM, Multichannel, Dolby Digital+)

Tried Shield audio settings (Auto, Manual, DD/DD+)

Hard power-cycled everything

Verified no recent firmware changes on TV or Shield

Problem persists even with brand-new high-quality HDMI cable

The issue now: Audio randomly switches from Sonos → TV speakers → back again. No pattern. No relation to ads (I’m on YouTube Premium). Happens on Plex + YouTube. Happens even after complete teardown/rebuild. TV out of support from Philips.

What I’m considering: Bypassing the TV’s eARC entirely using something like:

HDfury Arcana

HDfury Integral2 + Arcana combo

FeinTech VAX04101 or similar HDMI matrix/eARC converters

The idea is to route all HDMI sources (Shield + Switch) through an external switch/matrix and then feed video to the TV and audio directly to Sonos, skipping the TV’s eARC.

My question to the community:

If you’ve experienced similar eARC instability with Philips TVs or Sonos Arc, what fixed it for you?

Has anyone tried the HDfury Arcana or Integral2 with a Sonos Arc system — did it fully stabilize your audio?

Are there any other recommended HDMI-to-eARC solutions that work better?

Is this likely to be an HDMI handshake flaw in the Philips TV that won’t be fixable without bypassing it?

Any other ideas I haven’t tried?

Any guidance or first-hand experience would be massively appreciated — I’d love to get this system stable again without replacing the entire TV.