Are you saying that the AdGuard developers have not acknowledged this as an "official" issue at this time? It may not be AdGuard but what is the status of this from the developer's perspective right now?
Does this mean you always used Adguard nightly and never had this issue, or does it mean you had the issue in the beginning, then updated to nightly and the problem was gone? The latter case would be more of an indication that the problem is fixed in nightly builds.Are you on latest AdGuard nightly? So far I did not experience the issue on latest nightly in my Pixel 3 XL.
How long have you gone without a reboot? It seems that if you can get to two days, you are in the clear.Tried disabling "filtering of all apps" and didn't get any reboot since then.
I updated to nightly now, put it back to default and will check if it's fixed.