DEEBOT X1 OMNI stuck on error 406/10025 - Can't setup WIFI after working well for years

My DEEBOT X1 OMNI (purchased October 2022) was working fine until it randomly went offline in the app this week. After trying to redo the setup with WIFI connection, I've been stuck with error 406/10025. I've spent hours troubleshooting and may be tempted to try the UART root approach as a last resort, open to any advice or tips!

What I've already tried:

• Factory reset (held reset button until robot said "factory reset")
• Removed device from ECOVACS HOME app and re-added
• Cleared app cache and data, logged back in with a fresh account
• 2.4GHz only confirmed (5GHz fully disabled on router)
• WPA2-Personal authentication confirmed
• AP Isolation disabled (ASUS RT-AX86U Pro)
• Wi-Fi 6 (802.11ax) disabled temporarily
• Tested with a 2.4GHz mobile hotspot from a PC — same error
• Tried setup from Android, iPhone, and iPad — all fail
• Tried a brand new ECOVACS account
• Robot Wi-Fi light blinks correctly (confirms pairing mode)
• MAC address appears in the app during failed setup (so it communicates)
• Setup fails after 50% progress every time

Network hacking attempts:

• Connected Mac to ECOVACS_XXXX hotspot
• Found robot at 192.168.0.1
• Port 8888 is open and responds with HTTP 200
• SSH on port 22 refused (expected in pairing mode)
• Tried various API endpoints on port 8888... all empty or 404
• Could not intercept app traffic before robot killed the hotspot

Router: ASUS RT-AX86U Pro

I am open to anything at this point. I took great care of it and it's been working so well. Thank you in advance!