Good to know it's working again.
This issue is most likely caused by either a faulty internet connection or Apple's App Store framework (at its backend or on your Mac).
I found a retry after some time (and probably a restart of the computer) the most successful fix. Unfortunately this situation is beyond my control, and therefore not much I can do about it…
Edit: Just out of curiosity, are you using StitchBuddy's beta version via TestFlight? These days I encountered similar issues with Apple's test environment.