lobby: Counters of players in particular arenas are not updating

[CreeX0rZ]

Describe the bug
After idling for some time in lobby, the "Players online" counter updates the value correctly all the time. However, the counters of players in particular arenas are not updating correctly. The counters update themselves after rejoining any arena.

To Reproduce
Steps to reproduce the behavior:

1. Go to lobby & observe the counters of players in arenas
2. Idle for some time
3. After some time have passed by, compare the counters of players in arenas with the counter of players online (preferrably check after more people have left the server)
4. (Optionally) Join any arena > Go to lobby again & observe that the values have updated accordingly

Screenshots