Why did I lose all of my contacts after installing OS 10.2.1.3062?

Some contacts are still there. It looks like the ones that are no longer there are the contacts I had saved by selecting from a list generated by the Facebook app.

Example: when i would go to save a number from someone who texted me, I would tab the number to add it. A list of facebook contacts would auto-load in a list and I could select someone from that list if the number if they happened to be a facebook contact. Then I would select save contact in the next window.

The contacts I saved this way are the ones that are no longer on my phone after the last OS update. roughly 80% of contacts lost

I stand to be corrected, but normally the facebook contacts only get added to your phone's contact list when you log into the app and allow them to be synced, other then that they are not included in your list.

I dont believe there is a two way sync for facebook contacts, where the numbers you add to them on your phone will be backed up on facebook to their respective profiles or some facebook server. So if for some reason you delete the facebook app from your phone or remove your facebook profile from the accounts section, all those contacts will be gone.

I find the best way to keep contacts without having them getting lost is to add them as a new contact instead of selecting facebook. So you would add them to your local contacts, sim and any other options in the "save to:" tab. Then link all their profiles eg: bbm, facebook, twitter. That way theres no "duplicates" in the contacts app and all their infomation is under "one contact" for that person.

So if you your facebook contacts get removed again, the contacts number will still be on your sim card and phone memory and can be backed up through link and restored at anytime.