I recently purchased a new Deco XE75 Pro (V2.0) mesh system (3 units), setup in AP mode. Initially, the performance was impressive with my gigabit internet connection. The wired speeds were consistent with what my ISP provided, achieving 940/800 Mbps up/down. The WiFi 6 speeds (5 GHz, 160 MHz band, optimized channel) were also remarkable on the first day of setup. I was getting about 600 Mbps download on my M1 MacBook Pro, around 800 Mbps on a Lenovo ThinkBook, and even approximately 500 Mbps download on an iPhone 14.

However, the following day, I switched it to Router mode to bypass my ISP's modem. I encountered a significant drop in WiFi speeds, falling to about <400 Mbps across all devices. This occurred even after I attempted to reset the entire system and set it up again back in AP mode with ISP's modem.

Main unit was connected directly to ISP modem in AP mode, and SFP to Eth converter in Router mode. Setup was not changed, and I made sure during the speed tests, device was connected to the main unit, and it's on 160Mhz 5G wifi.

The only other notable change I made was upgrading the firmware to Deco XE75 Pro(CA)_V2_1.2.7 Build 20231011 from the original version, which I believe was 1.2.1 (I could be wrong about this number though). The website has only 1.2.2 and 1.2.7, not sure if I should revert back to 1.2.2. I saw the new beta version released on this forum but not sure if that's going to "fix" it.

I am seeking advice on what might have caused this sudden drop in WiFi speeds and how to resolve it. Could the firmware update be the culprit? Any insights or suggestions for troubleshooting this issue would be greatly appreciated.