think-cell uses Microsoft Graph to render labels whenever possible. Labels that cannot be created using Microsoft Graph are created as PowerPoint text boxes. At some combinations of font size and zoom level, Microsoft Graph and PowerPoint render text differently, resulting in an uneven look of a chart that uses labels of both types. The following screenshot shows an example:
In most cases, choosing a slightly different zoom level will eliminate the problem. If the problem persists even in slide show view, your only option is to use a different font size. Note that this problem is specific to the current screen resolution, therefore the same slide may look different on different computers. The problem does never occur on print-outs, because printers work at far higher resolutions than screens.