1) I'll need your saved games before a match with a problematic player
2) Is it with the latest version ? (SubBuild 2018.12.8)
I tried to reproduce the issue by watching 2 CPU vs CPU singles then 1 doubles, both in World Tour & Training Club, but no one disappeared... So I'll need your saved game as well (and Tennis or profile .ini).
4) I couldn't reproduce the bug, so they might happen once you have played the game for a while ; they might get fixed anyway once I'll have ported the game to the Unity engine, as I'm currently cleaning the menu system to make it a bit more resilient
3) 5) Fixed in today's update