Sometimes Microsoft calendar event not generated in outlook calendar

We are using Microsoft Graph API for creating events in the outlook calendar using Android. It works well but now sometimes it doesn't create events in Outlook Calendar and it also receives event invitations Mail in Junk Email. After updating that event now all events create properly.

We encountered this problem two or three times but I couldn't figure out the problem.No errors were found on the front-end side as well as the backend side.

Can anyone please suggest why this is happening?