Hello RamezFahmy,
Thanks for the info. Since it's randomly a contact here or there, it might be you are inadvertently tapping something to delete them, or an issue with the account they are with.
First, check what contact accounts you have: If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support
"If your contacts, calendars, and reminders are in iCloud, then iCloud automatically updates your information. If your information is in a third-party account, like Google or Yahoo, you can change your default account to iCloud. Changing your default account to iCloud won't move your existing information from a third-party service to iCloud."
This is a very common issue, where people do not know they are getting some contacts from a work email account, others from iCloud, and maybe even some from a third-party email account.
When they change their email account, or it needs the password updated, or they leave that job, all those contacts are removed because that old account is not longer syncing with the device.
Once you see where your accounts are coming from, turn them off. See what contacts get removed. You can turn them back on later. Or, go to your individual accounts online, like Gmail, export the contacts to a Vcard, then import them into your default account, or make iCloud your default, and import them all to iCloud: Import or export a vCard in Contacts on iCloud.com - Apple Support
Thanks.