Adobe Illustrator CC 2019 introduced a new UI Scaling preference to improve the usability on high DPI (i.e. 4K, Retina, etc.) monitors. However, MAPublisher 10.3 will only match the scale setting in the Mac System Preferences, not the UI Scaling setting in Adobe Illustrator. This means that when the Adobe Illustrator UI scaling setting is increased, the MAPublisher interface will appear smaller than the rest of the Adobe Illustrator interface.
A planned MAPublisher update is expected to resolve this issue.