This is typically caused by Auto Run being set to run too frequently.
In your Web Connector, either turn Auto Run off, or set it for a larger value. When it is set to off you can choose 'Update Selected" when you are ready to sync.
This error is caused by this value being set too low such as 10 min or less, and the Web Connector not having enough time to finish the previous task before starting the next sync. This causes the queue to stack up on top of each other which can prevent another task from finishing.
We recommend 30 or 60 minutes+ for the Auto Run value.