In patch 1.30.0, Tinker’s Cluster Rockets damage was changed from 11.25/18.75/27.5 to 11.25/19.75/30.5, which meant total damage of 4 intervals on each unit (if not spread) was increased from 45/75/110 to 45/79/122. But the text of damage value displayed on the tooltip of ability learning menu is not updated.
Just FYI, I think this is a bug with the underlying Engineer upgrade. The problem was introduced sometime during reforged. I don’t know why it hasn’t been fixed yet.