Good Morning, 

Thank you for contacting the U of M Extension Service. 

Please click on the following link from the Missouri Botanical Garden about redbuds: 

https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=280440&isprofile=1&basic=Cercis%20canadensis

This information states: 

Canker can be a significant disease problem. Verticillium wilt, dieback, leaf spots, mildew and blights may also occur. Insect pests include Japanese beetles, tree hoppers, leaf hoppers, caterpillars, borers, webworms and scale. Keeping the tree vigorous by regular watering, fertilization and pruning out dead branches as needed will help keep the tree healthy.

Your photo of the insect is a leafhopper. Here is a link about how leafhoppers spread diseases: https://blog-fruit-vegetable-ipm.extension.umn.edu/2021/06/leafhopper-watch-hot-weather-and-aster.html

Although your tree is probably not susceptible to aster yellows, the leafhoppers transfer disease. 

Here is another link to verticillium wilt: https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/cankers/verticillium-wilt

With the wet weather we've been having it could be mildew or a blight. I would wait to see what happens as the days warm and dry out. As stated above, keep your tree healthy. You might consider adding wood mulch a few inches away from the trunk around the base out to where the branches drip the rain (drip line). The mulch will keep the soil cool and moist and protect the roots of your tree. 

Good Luck!