Expected Behaviour:
PiHole v5.0 (Docker Desktop 2.3.0.3 on MacOS Catalina 10.15.5 connecting to a HG659 router) works, iMac always on, serving DNS to all requests on the local network. Little maintenance required. Used the following instructions to install/configure PiHole:
"How to Run Pi-hole on Your Mac"
Actual Behaviour:
PiHole ( or something ) stops DNS resolution for some devices. Web interface goes down if I log out my user on the iMac... but some devices still get to websites fine. e.g. the Nintendo Switch ( connected to the router ) might say something along the lines of "DNS resolution is not available". When the problem happens.... if I log onto the iMac (using the user used to install pi-hole and Docker) .... then pi-hole starts working again. It seems as if ... when another user logs in, or my user is logged out, then PiHole (or Docker or something else) can stop working.
Debug Token:
Most recent debug token is: https://tricorder.pi-hole.net/gfpov54eie ( when working fine )
Because if I log in to the iMac... it's fine... I cannot generate debug when it's not working 
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I'm new to PiHole so apologies if something stupid done. Anybody have a possible solution or a workaround ? Thanks in advance. I expect this is not a PiHole problem... but if you can send me in the right direction 
BTW. I love this App!