So this is a multi-part question and it is complicated by some annoying things about my network topology. I will give a verbose question, but one can skip to the bottom and read the following details as needed.
I have a router on, say, 192.168.1.1/24 not running OpenWrt and NOT running a DHCP server. It connects to a computer on 192.168.1.2/24 which runs a DHCP server and dns requests route through this device.
I recently installed OpenWrt firmware on a spare router and intended to use it as a repeater to increase coverage for the 192.168.1.1 router. I attempted to configure it myself however after much frustration I reset the device's settings and followed this guide: https://openwrt.org/docs/guide-user/network/wifi/relay_configuration to the letter. I succeeded in giving my OpenWrt device it's own subnet 192.168.2.0/24 and make a bridge relay device which listens on 192.168.1.3. The router could ping websites when configured this way so all seemed well, and I could access the Luci GUI by navigating to the ip of the bridge in a web browser.
Now the problems started:
1.) I noticed that the signal strength on my iPhone wasn't particularly strong so I attempted to disconnect and reconnect it to the wifi network, disaster! Now it can't seem to find an ipv4 address and shows up as 169.* on the network. When I try to manually assign it an ipv4 address on the iPhone's network settings it still can't connect. There were no such problems before I configured my repeater.
2.) I fussed around a bit in the OpenWrt router settings to see if something might be wrong (e.g. incompatible encryption or bad channel settings, etc.) really just pawing around in the dark due to my limited networks knowledge. I saw a setting called something like "enable upstream ipv6 forwarding" on the wwan network interface and decided to uncheck this on the hopes that it would at worst not change anything (the repeater and the host network are only meant to assign ipv4 addresses). Disaster again! When I saved this configuration my OpenWrt device became completely inaccessible via ssh or the Luci interface. I can still see the bridge device at ..***.3 where it should be but all ssh requests to it time out.
First: can someone explain to me why changing this seemingly inconsequential setting caused my router to go dark on me? This seems to happen quite often when I reconfigure its settings and it's a HUGE PITA to connect via ethernet on its subnet and reconfigure it every time I change anything.
Second: does anyone have any idea what might be going on with the first problem, i.e. why adding the router as a network repeater caused my iphone and other small network devices to be unable to connect to the network as a whole?