how do prevent New Events in Calendar from auto delete data and the time reverting to default?

Just a general rule you may already know, for odd glitchy problems:

1. Run Disk Utility > Repair permissions

2. Command R boot and run Disk Utility > Repair Disk

3. Reinstall the app, then go back to step one.

4. Command R boot, reinstall system.

5. Command R boot, restore from Time Machine backup.

6. Throw laptop into garbage, wonder into northern wilderness to live off of land, wrestle for your life with angry mother polar bear, and all other problems will seem minor.

7. Arrange to have body cryogenically frozen, suicide, and be revived several millennia in the future when all technology glitches have been addressed.

8.... Well there are others but try these 7 first.

I am not an expert and do not know how useful these are with modern OSXs, but at least they will keep you busy.

had this issue. if using iCloud to sync, go to system preferences-icloud, uncheck iCloud calendar, wait minute and recheck, this worked for me.