Comment 19 for bug 1794553

Ok, this seems to be pointing at a problem with the apparmor profile. I'll prepare an update for that.

This is the patch I will be using:
--- etc/apparmor.d/usr.sbin.squid
+++ etc/apparmor.d/usr.sbin.squid
@@ -3,7 +3,7 @@
 # vim:syntax=apparmor
 #include <tunables/global>

-/usr/sbin/squid {
+/usr/sbin/squid flags=(attach_disconnected) {
   #include <abstractions/base>
   #include <abstractions/kerberosclient>
   #include <abstractions/nameservice>
@@ -18,6 +18,7 @@
   # alternatively include the <abstractions/ssl_keys> abstraction, which
   # gives read access to the entire contents of /etc/ssl

+ capability net_admin,
   capability net_raw,
   capability setuid,
   capability setgid,

If you want to try it, please change /etc/apparmor.d/usr.sbin.squid as per above, and reload it with this command:

sudo apparmor_parser -r -T -W /etc/apparmor.d/usr.sbin.squid