Yeah, I think I can partially explain what you're seeing there. GL's GUI isn't fully sync'd with the same capabilities as LuCI or the underlying uci. Here's another example:
Yup. I noticed the same thing on my Slate AX. Use one or the other. I recommend LuCI so you can set a proper .internal domain name. Who doesn't like https://router.freebird.internal?
It'd be nice if GL.iNet tried moving as much as they could from custom scripts to instead make appropriate uci show/get/set calls/pushes. IDK why they want to recreate the wheel.
Pull a backup of your current state then start experimenting. You can always restore via LuCI:
Weird. I hate to say it but I'd nuke it all & start over. It ain't much but here's something handy to help save states as you build up a clean config:
#!/bin/sh
HOST="$(uci show system.@system[0].hostname | cut -d "'" -f '2')"
DOMAIN="$(uci show dhcp.@dnsmasq[0].domain | cut -d "'" -f '2')"
timestamp="$(env TZ=UTC date +'%Y%m%dT%H%M%Z')"
sysupgrade --create-backup /tmp/backup-"${HOST}"."${DOMAIN}"-"${timestamp}".tar.gz
exit 0
Throw that into a script file & run it as a check point any time …