Xcode 9.4.1 won't debug since power outage

I was running Illustrator CC 2019 in debug mode, working on a plugin using Xcode 9.4.1 when the power went out. Once the power came back and several times afterward, I've tried to run in debug mode, but Xcode died with the message "could not attach." The very same project and source files work perfectly on another Mac running the same OS (Mojave). Removing and re-installing both Xcode and Illustrator haven't helped. Has anybody else experienced this? Any suggestions would be much appreciated!