The skip_sync field not only exists on assets but also on the cmdb table. It is the flag indicating whether synchronization between Asset and CMDB can be skipped (see the documentation: CMDB table attributes description).
There are OOB script includes and business rules that may invoke according functions and change the value of skip_sync:
The skip_sync flag is used to prevent recursion within the same cycle of business rules and will be reset in the next cycle during Asset-CI synchronization. The skip_sync flag is set to false by default.
As the two business rules above would be triggered twice during an Asset-CI synchronization. The skip_sync flag would be set to false again after the synchronization. In case the skip_sync flag was set to true for some reason, an update on the Asset/CI should help set the flag back to false.