I got the following error, which I couldn’t reproduce
(bf4211523baf8ab1c853aac48ef0324f8f704510).  Is there a need to worry?

+ guix build hello -d
+ grep -e '-hello-[0-9\.]\+\.drv$'
accepted connection from pid 15177, uid 1000
guix build: error: build failed: substituter `substitute-binary' died unexpectedly
238 operations