It's perfectly normal at this time of year, especially when grown in the cooler parts of its climatic range, e.g. on the Blue Mountains escarpment where I see a lot of them. Jacaranda is a dry-season-deciduous tree, which translates in our climate to losing its leaves in early spring and getting them back at the start of summer, in the middle of their flowering period.

The 'branch' that you say falls from the trunk is actually the rhachis of the bipinnate leaf.

You can tell when a branch is dying or merely becoming leafless by digging into its bark with your fingernail to see if it is alive and sappy below the surface.