@sgulyan 

I'm having this same issue.   After updating my firmware to 1.2.7 Build 20230620 REL 31797, all three of my X55 Deco's are seeing a SEVERE drop off in throughput.   Testing on wired network produces accurate upload/download speed through my router, however the moment you switch to wireless connectivity (after optimization, etc.), the speed drops off, by approximately 90%.

A complete reboot of all three decos, seems to temporarily improve speed, but that is short lived, and within hours the throughput is again reduced to about 90% of what the bandwidth should be.

I'd like to downgrade my firmware, to get back to a stable/useable wireless network.

Thank you.