I think your problem lies because you upgraded via Luci. The adguard home build included in the firmware is made to work with the firmware and is only officially updated via the Devs when they release a new FW build. The Devs disabled upgrade checks / updating due to not being fully tested per release. So it's been advised to just stick with the current release that's included.
There is however a script that has been made to upgrade adguard home. You could try and run the script and see if it will overwrite and fix your problem. Failing that you would need to reflash and then if you want to upgrade adguard home again just do it via the script and not Luci.
Script thread: