I personally observe with my own eyes many many times where Android turns off Adguard’s VPN for a split second when doing various Google things like receiving messages in Google Messages.

I haven’t been able to pinpoint it but my observation is that the disconnect/reconnect happens when a connection is trying to be made (ex. RCS message incoming), and I suspect Android is dropping the VPN to make its own connection. Sounds paranoid, but I’ve been carefully watching it happen for a long while.