Hello, I recently encountered this problem with my brand new RG35XX-SP running 2508.4 Loose Goose. I didn’t change anything in “Network Settings”, just entered my ssid and password.
I don’t know if it’s the same issue you’re experiencing, but I found a discussion on Reddit suggesting it might be related to WPA or the frequency band.
It turns out that for the same Wi-Fi router, I can have multiple SSIDs with different security protocols. By switching from my Wi-Fi (WPA2/WPA3, 2.4 GHz/5 GHz) to another Wi-Fi (WPA2, 2.4 GHz only), the RG35XX-SP now connects quickly and without any problems.
Previously, I had a very slow initial connection, random disconnections, and web services like Syncthing or SFTPGo wouldn’t launch on startup.
The connection is now stable, I’m able to download 5,000 covers with BoxArtBuddy without any issues and web services start at boot.
EDIT: my bad, it was not on Reddit but on this forum [2508.4][RG40XX-H] WIFI disconnects after 20sec - #3 by mathiasxii