Hi Jitsi team!
We do experience the same issue. Sometimes our users use a room in the span of several days and as a result there are sometimes 5-6 ghosts just hanging around and one of them is the room admin, so we cant even kick out those ghosts.
These ghosts are usually appearing after a user is being disconnected (mobile or browser) without explicitly leaving the room.
We have a vanilla/quick install on Ubuntu 18.04 installation.
sudo dpkg -l | grep -i jitsi
ii jicofo 1.0-508-1 amd64 JItsi Meet COnference FOcus
ii jigasi 1.1-38-g8f3c241-1 amd64 Jitsi Gateway for SIP
ii jitsi-meet-prosody 1.0.3729-1 all Prosody configuration for Jitsi Meet
ii jitsi-meet-web-config 1.0.3729-1 all Configuration for web serving of Jitsi Meet
ii jitsi-videobridge 1126-1 amd64 WebRTC compatible Selective Forwarding Unit (SFU)
Please let us know if we can help you with debugging.