@GHeys I have X60 with the newst firmware and still having the issue

I too was experiencing this issue, yet my network appeared to be working properly.

My three units were ordered as a 3-pack "TP-Link WiFi 6 Mesh WiFi AX1800". The Deco I could connect to is the one with the wired connection (i.e. the base one). I did perform the offered firmware upgrade and It reports F/w version 1.2.6 Build 20201013 Ref 58271. Green lights are on the two Decos that were allegedly disconnected and during the firmware upgrade their lights went red, then back to green as though they were actually connected to the mesh despite the report. 

After doing the update, I then disconnected the power cord for 30 secs and replugged it. The unit furthest away from the base then became "connected" but the same process on the other did not seem to affect it. Then Deco app announced that a unit had out of date firmware so I told the app to do that. So it downloaded again. I am not sure (at that point) whether the newly connected one had been updated or not, or if that was the one reporting it was out of date. I suspect the latter as otherwise how would the app know one was out of date.

Now all three have reported that they are connected and have up to date firmware. So I am not sure what was "wrong" initially, nor which of the things I did to make it go away was what solved it. I only document my experiences here in case it offers ideas to others. Good luck!