I had the same issue with XCode update. Today, the download finally started, progress bar reached 100% then... XCode was not installed. Infuriating. Too bad Microsoft don’t allow easy access to LTSB and destroyed Windows UI. I feel the state of commercial OS declined sharply in the last decade.
Something about Catalina has been causing issues with both installing Xcode and massively increased phantom disk usage (not just related to TimeMachine). I didn’t experience the former (have colleagues who did though), but did experience the later and had it self correct (on a machine without TM enabled).
