They are aware of this issue with the Grand Soiree and will be pushing a new server patch out tomorrow to resolve this issue.
The event challenges can still be viewed by checking the right side of your map screen while in a match and your progress and rewards you've earned through the Event Challenges will be rewarded retroactively.
You can find more information here:Apex MegaThread - Grand soiree Issues
Need help? Mention me with @Zeelmaekers!
Having technical issues with Apex? Check out this Troubleshooting Guide
"Alone we can do so little, together we can do so much. #AnswerHQ"