I can't tell you what the reason is but it resolved itself after a while for me. I'm assuming iCloud finished syncing something and some deadlock between Xcode and iCloud was lifted afterwards but I can't be sure.

Hi and thank you for your comprehensive response. I added fflush(stdout) after my printf statements and that resolved it, so I believe you were right about the buffering being the culprit here. Are there any downsides to using fflush(stdout) I'm unaware of vs. setting the STDBUF environment variable? Thanks again!

Thank you very much for the swift response, I will!