I have in the mean time solved it by using the TFPT method explained at https://www.tp-link.com/nl/support/faq/2958/ They are now all up-to-date to 1.5.3 and everything seems to work flawlessly...

And when I tried it a second time the same Deco that updated earlier did a reboot.

I did everything via the web UI

@TP-Link I first tried the oldest version. The message I got was that I should use a more recent version of the firmware (I suppose because 3 of the 6 Decos have version 1.5.1.), I then tried the...

Can someone provide me with a reply plz?

I recently bought a bunch of extra Decos so increase the Wifi quality in my house. They have two different Firmware versions (1.1.5 and 1.2.3), whereas my first three Decos have version 1.5.1. When I...