can't connect to my new router

I’ve been using Volumio on a Raspberry Zero W (with internal wifi) for months, without any problem.
It was connected to my house modem/router.

Now I’m trying to use the same Raspberry on a different location, where there is no internet connection, but luckly I got a spare wifi router that I can use as a bridge between my phone/tablet and Volumio webgui.
So I set up the wifi in this spare router and called it “Volumio bridge”, using the password “volumio2” just like on the hotspot.

I can access to the Volumio hotspot using my phone, but after I connect to “Volumio bridge”, Volumio does not turn off its hotspot and does not connect to the router. I can connect to the router using my phone, so the router seems fine.

What am I doing wrong? maybe Volumio can’t connect to a router if there is no modem/internet capability?

ps. this is the router that I’m trying to use: … izard.html

update: I connected the router to internet using the WAN port and a modem, but Volumio still doesn’t want to connect to it. (and yes, using my phone I can surf the internet, so the router can go to internet).
so the problem is not that Volumio needs an actual internet connection, instead it must be something else about this router.

also, while I was testing Volumio on a proper WIFI network, I noticed that the web GUI is not working properly: for example, the time bar is stuck and doesn’t update by itself, unless you refresh the page, and the whole GUI is slow and unresponsive.