Some contacts were deleted

[drfirro]

Please I need help regarding all of sudden I found some of my contacts were deleted! Thanks

[Lakii_]

Go to Phone > Contacts > The three dotted button > Deleted contacts

[PROFXs]

This to recovery contacts try it

[Pioneers]

From 5 months tell now, my contacts suddenly deleted. I tried the restore from the Samsung Cloud many times without success then suddenly the contacts began to restored not one time but in stages. 

I want to know why the contacts suddenly deleted and suddenly restored, how to prevent that and how to restore the contacts? My mobile is Samsung Galaxy M62