@Kevin_Z  Wow didn't realise there was a new Beta out. Look forward to trying it out when I get home. Thanks. 

  @Kevin_Z 

To narrow down and analyze my issue with Archer BE550 (Archer BE550 problem with autonegotiation / autosensing to Deutsche Telekom MagentaTV One), I also received this BETA firmware for debugging and logging and can confirm that the current Tether app for Android shows exactly the same behavior for me.

The check via the web interface works without any problems and shows that I am using the latest firmware.

  @Kevin_Z 

Hi Kevin, thank you for responding and Best Wishes in New Year.

About my issues:

I didn't say that my both BE550 are connected via EasyMesh. They works on different and separate networks, but I did firmware update to latest beta on only one of them and now Tether app showing error "Network Unstable" when I checking firmware update for that router. On my second BE550 with firmware 1.0.12 everything seems to be OK. If you ask me about my connection and strength of signal - well...I didn't monitored it with any specific software because to be honest all good software for monitoring WiFi are for mobile phones, where my WiFi looks OK for me or I didn't realize any special problems, (probably) because I don't download any huge files via my mobile phone. The problem is in my PC, the computer is 3m from the router and now I see big difference between firmware version 1.0.12 and 1.1.0 beta. As I said previously - after update the connection becomes unstable when I start transmitting a large file (no matter download or upload) and as I realized router changes my band from 6GHz to 2.4GHz, so decreasing speed is obvious. It never happens before on firmware 1.0.12 and my speed always or almost always was 5.7Mbps on 6GHz band and connection was very stable. Unfortunately I haven't screenshot for a proof, but now my maximum speed very rare reached 5.1Mbps, so obviously something was broken in new beta. Below my screen from actual connection.

Installed the new beta but lost connection to the internet afterwards. I needed to do a complete power off for the BE550 and ONT box. Once started it connected fine. 
 

I can also confirm the Tether app showing a network fault for firmware check. This is on IOS beta 18.3. 
 

so far everything else looks good and working fine. 
 

Been running for around 3 days now then randomly it just stopped working no wifi network showing up done a reboot after realising waiting 10 minutes to see router would sort itself out lost connection with some devices after reboot.

I have technical question...How to understand this message from 1st post: "Once upgrade to the 1.1.0 version, you cannot downgrade back to the 1.0.x firmware" ?

I mean - Once I upgrade to the 1.1.0 version, my router allow me to do downgrade to version 1.0.12, so ? But I'm still not sure if the older version completely replaces the new one, because router show version 1.0.12 but he acts like he has a new one. Need more tests, just don't have time now.

  @sahin76 @Kevin_Z 

Kevin on this beta you can log into router when its active as easymesh sattelite :) 

Form bugs/problems i notice in easymemesh sattlite mode:

- WiFi 7 (6GHz) performence problems (low speed connection between main router and clients) showing high speed but going much much slower. 

- Abnormal USB sharing = slow speed transfer and subfolders bug (when you unselect subfolders in usb sharing, you lose premission to send files to disk)

I already send that to TP-Link enginner via email with BE800 Abnormal Sharing problems. But maybe others have same problems so they can confirm that. 

  @Kevin_Z 

Is there any information as to when the BETA firmware will become the final firmware, or at least a time frame?

If not, when will the errors mentioned here, such as the update check not working in the Tether app, be fixed and there will be an updated BETA firmware?

  @GrenSo 

I keep contact with TP-link Enegnier via email and i ask him about that. If he answer i will let you know. 

In my opinion probably not soon, its a lot things to fix and updates. I think first they want fix BE800 and after they will care about BE550 because both works on similar chip. So when you will see new official firmware for BE800 after that should be for BE550. But i can be wrong :)

But @Kevin_Z  maybe can know more details and share it with US ^^

I have already bought the BE800 model, updated latest beta firmware and Tether app also can't check firmware availability, so as I said before, seems to be a Tether app problem, because I have same Error as BE550 with beta firmware. Also in BE800 with latest beta firmware, option "Aggregate LAN" disappeared from settings.