Firstly yes, the WiFi on the Hub 3, and indeed all of the hubs isn’t exactly stellar. The message you are seeing would indicate that the web server on the hub has fallen over, if it really wasn’t responding at all on that IP address then the message would be different.
OK what you probably need to do is a full factory reset of the hub, which is done by sticking a a paperclip (or similar) into the reset hole on the back of the hub, leave it pressed in, and you will ‘feel’ a click as the button is depressed, for a full 60 seconds, the hub will reboot itself and come back up as it was when first delivered.
Log into it using the password on the sticker on the bottom, you did check to see that the sticker was there and legible first, no? It’ll be back in router mode and accessible on 192.168.0.1, pop it back into modem mode, reboot and all should be well.