Some people not present in server list and not synced with the members on the right side

Same for me, on Mac. Private server, some roles setup. People disappear entirely when they're offline and the "members" page is sometimes entirely empty, sometimes populated randomly, with some people showing up and others not, and it's got nothing to do with offline/online status. Some kind of caching issue, maybe? I can see people offline in my friends list, they show up as grey icons. In the server, they're just gone, not listed in the sidebar at all.