. Just go Settings > Account > Google and toggle the Contacts Sync switch to on. Here is another tutorial to backup contacts android
Visit my YouTube guide for step by step guide
OK i have ??? a solution.
The problem is depended on phone's ram. If you have 1gb ram, then each of your contact must not have more than 100 contacts. I splited contacts with many numbers to 2 or 3 parts, with less of 100 numbers each, and now sync is working fine.
Interesting! Thanks for sharing that, Lazaros.