Argon can't join existing mesh

So it’s kinda stupid question to ask but I can’t access the “Select mesh network to join” page when setting up a new argon.
First of all, after setting up the first argon following the instruction on the app (scan sticker - update OS), the app would enter a forever loading screen with the LED blinking in Listening mode. If I cancel/exit the setup and scan the sticker again, I could continue the setup (connect to wifi - name device - create mesh).
Then I had to repeat the same process for my second argon (also forever loading screen issue). The problem was, instead of getting the “Select mesh network to join” page, I was directed to “Create a new mesh” page again. So pretty much I can create many mesh networks with these argons being gateway devices, but none of them can join existing mesh.
I have 5 argons and this issue persist, so it’s definitely not a hardware issue. Any suggestion or hint is appreciated!

The HA (high availability) network feature which allows multiple gateways is not yet implemented and that's what the answer was to similar questions in this forum
Argon to Argon Mesh Setup
Multiple Gateways
2 Argon boards on same mesh network?

However, recently a new "feature" was added which should enable you to add an Argon as pure non-gateway node (without its uplink capability).
However, not with the app but via CLI

This is the post talking about this option