This is a UITableView separator string. You can remove it by setting it to None.
Goal C:
self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
Swift:
self.tableView.separatorStyle = UITableViewCellSeparatorStyle.None
Initially, the separator line is not visible, because I think the height of the image or view added to the cell is greater than the height of the cell.
And that is why the dividing line is visible during scrolling. If you are testing in Simulator, use Debug> Color Mixed Layers for Simultor. This is useful for tracking overlapping views.

Edit:
IOS 8.0 introduces layoutMargins for UITableView . Therefore, this may be the reason.
See the answer for more details.
He explains to clear layouts by setting cell layoutMargins as UIEdgeInsetsZero .
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