This is a relayed information from several reports and different users.

1. User click on event Mail and the body of the Mail is not shown. She had to wait a long period of time. Sometimes its only white and sometimes there is the screen showing "waiting for loading". Mostly this happen with event Mail. Working cost too much time. She don`t pull in intervall time, but manually. Maybe the problem is, that kontact loads all calenders on each invitation mail. That makes things really slow. We have many users with a lot of calender subscriptions and with this setting its not usable.
2. This would be for event invites? It also takes a long time for me for Kontact to actually show me the box to show event information with the option to accept/deny and so on... typically 5-10 seconds. Can you check whether it is just slow or malfunctioning? (both need addressing, but let's narrow it down) The "waiting for loading" I generally see when you did not give it time to actually show you the box, it seems to block the queue so that even when you select something else it is still waiting for that first job to finish. (FWIW) (So if you click vigorously enough, you should be able to cause a long delay by jumping between different events, filling the queue with backlog, I guess)