Issue #659 is reappearing again, i.e. $SYS/broker/clients/disconnected is -1

[phit42]

I am running the latest eclipse-mosquitto containerized (linux/amd64, ENV VERSION=2.0.18 DOWNLOAD_SHA256= d665fe7d0032881b1371a47f34169e...), and am monitoring it with uptime-kuma on for example the "disconnected" value.
It appears the issue as mentioned in #659 and further in #287 has reappeared again, as the value of disconnected infrequently steps to -1. (see screenshot) Which according to a comment in #287 is not supposed to happen.
Now I am definitely not an expert, so I might have misconfigured sth, but it seems straightforward.