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From the looks of it, I think there is no styling problem here. I think the issue is when you put the labels at the bottom, on the first chart, which has 3 labels, they break into 2 lines as the second one that has 2 labels stays in 1 line. So as the canvas is generated it fits the chart to the space available.
Please leave only 1 label on both charts and see if they are the same size then.
Source:stackexchange.com