Has anyone else had this issue with AdGuard Home:
AdGuard has been updated from 107.5x to 107.59.
For Version 107.57 I can open the settings page, at port 3000 as expected, I could on earlier versions as well.
For Version 107.58 and 107.59, the settings page times out before opening. I've tried it at the default port 3000, and by modifying config.yaml opening it at a different but available port as well.
The problem appears to be with the AdGuard executable file itself.
Sounds similar to what I'm seeing too, had to downgrade for AGH to work again.
I have upgraded my AGH to version v0.107.55
I think it gets "broken" from version v0.107.56 because from then they are changing the HTTP API. (not tested yet).
No problem here with last version, all the settings "taps" working like always 
Adguard installations that come with the GL firmware do not show the update icon unless you go and remove the --no-check-update tag from /etc/init.d/adguardhome (around line 69). If you do, and allow updates from the GUI, there's a chance that a future update will breah AGH.
If this happens, you'll need to downgrade AdGuard to whatever version came with the firmware by ssh into the router and typing
rm -fr /etc/AdGuardHome/*
cp /rom/etc/AdGuardHome/* /etc/AdGuardHome/