Just to let you know, I pushed an update. I don't really think it will resolve the annoyance with AGH built-in .yaml checker, but it might.
https://github.com/AdguardTeam/AdGuardHome/issues/4067 is just one of the past annoyances I tracked down with the .yaml checker. Ultimately, any bugs in it need to be resolved by the AGH team. That is one of the reason's I have it move the yaml to yaml.err. The problem with the installer is, it will only attempt to let you reconfigure on the first ".yaml" check failure. It then performs another check at the end of reconfiguration, if it fails again you have to rerun the entire reconfig option. This is just a consequence of the feature. The intended purpose is to actually determine the root cause of the break in the yaml.err. Sometimes it is a "schema version" disagreements, other times adguardhome has added or changed a setting in the .yaml file which breaks something. I usually have to add drop-in's to the installer to band-aid the issue.
Next time you run into a problem like this, you can actually check the error yourself using the AGH checker from the command-line
Code:
AdGuardHome --check-config -c "/opt/etc/AdGuardHome/AdGuardHome.yaml.err" --no-check-update
It will output, what's causing the problem if there is one.