Hello ,
Some people are experiencing some lagg from time to time, for me personally I have been disconnecting and reconnecting and some of my friends have been rubber banding and we also see people rubber banding sometimes also, I'd say it's the server being unstable from time to time maybe. For me the lagg has happened when there have been 4000 players in the server.
Although these days I haven't had much issues so it may have been fixed a bit, but experiencing lag spikes is common on a 4000 player server