After upgrading Magento from 2.1.8 to 2.2.1 in admin section some of tab blank.
If I comment below line from system.xml then it show again but no data save in database.
<!--<backend_model>Magento\Config\Model\Config\Backend\Serialized</backend_model> -->
I encountered a similar problem with a 3rd party extension. I believe your 3rd party vendor (in this case VES Theme) did not upgrade their extension to be compatible with 2.2 yet. You will most likely see an unserialize error message in your logs as well.
The reason is, that unserialize was replaced in Magento 2.2.
See: Magento 2.2 Backward incompatible changes
This release replaces usages of unserialize with json_decode.
Case 6: Your extension uses a backend model that extends \Magento\Config\Model\Config\Backend\Serialized to save/load data to/from the database.
Solution: Write an upgrade script to update data stored by the extension in the core_config_data table from serialized to JSON format.
Contact the extension vendor to fix it.
