Changing network-control to network-observe results in the following AppArmor denials being logged.
Oct 9 10:13:26 skull kernel: [605716.737513] audit: type=1400 audit(1507540406.053:33011): apparmor="DENIED" operation="capable" profile="snap.discord.discord" pid=27153 comm="Discord" capability=19 capname="sys_ptrace"
As far as I can tell the application works correctly using network-observe. I’ve updated the opening post.
As for exitting Discord, if I use the Indicator and select quit the application closes correctly.