Multiple users are having issues with resources and appointments. Why?

Hello, I'm experiencing different issues with Outlook and Exchange and I think listing all the issues at once may be helpful in seeing if they are interconnected. I have 3 different users with 3 different problems when it comes to resources. One of my users books a room, it shows up on the calendar but then it stays at tentative, so other people can book over the appointment. Another user gets a blocked message when she tries to book a room, she hasn't had this issue before, we can't pinpoint any recent change to trigger this. Another user has a deleted appointment that keeps on recurring and we can't seem to find any specific pattern. I'm fairly new at this so I can't seem to find the logs on the exchange server and I wouldn't even know what to look for. Any help in the right direction would be nice. This is also my first time posting on this site so if I should break down the questions or any other tips/rules I'll be glad to follow them. Thank you.