I've just swapped my router out so I've had chance to play with the old one more now. It was suffering reboots. I could almost guarantee connecting to LUCI using Edge would crash it. It was also at random times outside of the GUI use as well though.
I reset to defaults and still suffered the same issues (I have a separate post on some of it).
At the moment I've just switched it back to the standard OpenWRT software (OpenWrt 19.07.3 r11063) and have found Edge now works. I'm not sure why but seeing as pretty much everyone else has no issues, then it is probably something with my hardware going awry.