@TP-Link_Deco Ok, I thought there was a new firmware since this one.  This one still does not work.  Please see my post #24 on this forum.  Also, please stop marking that beta as a solution.  It does not fix the issue.  I am still rebooting both slave units every morning.

@imikem 

It the same beta

@imikem hi

I have the sameproblem. 
For me the deco in the bottom is WiFi connected and the other one in the middle is Ethernet connected. I thought that was the problem. Is it always the one in the bottom I mean are both of your decos Wi-Fi connected? :) 

Do this beta work in every country like for me in Sweden? (Tp-link often want us customers to use the correct Geographic version.)

@SJ2 

I've also had exactly the same symptoms with the X60s and with the upload of the .bin getting stuck on the upload.  I closed the browser (Chrome), flushed its cache and a subsequent retry has enabled me to upload the beta of 20200707 ok.  It's been uploaded for just over an hour now, so will see how it goes.

@TP-Link_Deco I just installed the beta, I will keep you updated. 

I just updated too.
I'll share my findings/thoughts here.

:)

I'll do the same. Just updated the firmware and will give it a day or two before giving update.

Test for about 3 days before you provide an update folks.  I have had my slaves go offline with this new beta as soon as 12 hours, and as long as almost 3 days.  For me, it still occurs although it is less frequent.  I'm hoping you have better luck so I can then just RMA my units and put this behind me.