Contacts not synchronizing to mobile device

I recently unlinked my android device from my zoho account, deleted all my contacts from my mobile device and zoho contacts, then imported my backup (a VCF file) directly into zoho contacts.

This worked fine, all my contacts were restored there. I then re-linked my zoho account but the contacts were only partially synched: 80 out of 209.

Any reason why this might be happening? The contacts to not contain any non-alphanumeric characters, apart from punctuation and hypens.