Leaf-spotting diseases or symptoms manifesting of damage from infections earlier in the season is not uncommon this time of year and is rarely of concern for overall plant health. We do not see any symptoms that indicate a serious issue here, and no treatments are warranted (or effective at this point). Losses of Redbud can occur from issues not specific to the species, such as over- or under-watering and infection by opportunistic pathogens due to drought stress or injury to the bark. (Trees surrounded by lawn that are not protected with a sufficient mulch ring are more vulnerable to lawn mower / weed-whacker strikes or herbicide contact, all of which can result in serious and untreatable sapwood damage.) Wood-boring beetles can also target stressed trees, and their tunneling damage will cause dieback or tree death. Which of these potential issues caused the loss of your neighbor's tree we cannot determine, but the presence of leaf spots on each would be coincidental. Weather conditions play a large role in disease severity and spread.

As we move into fall, continue to monitor your tree for watering needs, soaking well as necessary but infrequently enough that the surface soil layers are not staying soggy. Here are general tree/shrub watering guidelines: https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs

Miri