Since the last update (2.99.2909 to 2.99.2910 on Mac OS X 10.15.7) the month names are changed to number in the raster image export – see PNGs attached:
Hello, in my tests 2909 and 2910 work the same way. The difference between these screenshots is in the start date of the viewport. The first screenshot starts in December and the first month label is December which fits into its span. On the second screenshot the start date is November 30. November label did not fit into its span, and was replaced by the month number, and the formatting of all the remaining labels were changed accordingly. This is the same behavior as in GanttProject 2.8.11.
It is probably a bug that the same formatting is used for all month labels, but it is not new. We’ll look if it is easy to fix and if it is, then we’ll fix it in the next update.