UITableView stops scrolling when adding new rows

I just found the problem: After the new data arrived I had a UIRefreshControl calling [self.refreshControl endRefreshing]. And for some reason that method stopped all scrolling animation in the table view.

By adding

if ([self.refreshControl isRefreshing]) {
    [self.refreshControl endRefreshing];
}

the problem was solved.

Swift 5:

if self.refreshControl.isRefreshing {
    self.refreshControl.endRefreshing()
}