Sorry for writing in English.
I’m having the exact same problem with my HomePod Mini. Every other time that I try to use it, Siri says to me that it cannot connect to the internet.
The problem is the GigaBox, NOT the signal. I put the HomePod mini on the same table as the GigaBox, but the problem persists.
I also notice that within Apple iOS wifi settings there is a privacy warning. I believe this is because the GigaBox doesn’t use WPA3 Personal for security.
I really don’t want to buy another wifi router, since I only signed my contract with UPC 2 months ago. But, if that is the only way… 🙁