As a developer you find out that Apple hates errors. They somehow have come to believe that "it just works" also means that "it does not complain". For example, iTunes for its whole life would not report audio transfer errors from CD. So importing CDs was "it just works" even if the imported audio file had glitches.HTTP status code 503 is Service Unavailable. It sounds like a scaling issue to me. Too many users and not enough iCloud servers? Regardless, one would think Apple's iCloud API would provide an exact error message whenever this happens, so developers can respond accordingly in their apps.
Apple also considers its servers and services errors as potential security leaks, so they only report generic errors. This is a design feature at Apple to address security.
In Apple's log implementation all variable data in the log message is redacted automatically. A dev in control of their own machine can change that right now, but that is why I believe that no one is using Apple's logging but Apple.
I could go on and on. The truth is Apple does not want error messages displayed because it potentially harms the user perception and by default in a lot of cases Apple just ignores them and fails silently. After all if you don't get an error it can't be Apple's fault now can it?
Apple iCould APIs do not let the developer know what is happening in a way that is easy to use. If you have time to write 10,000s of lines of code you can figure it out, but most don't. iCould version 1 just never worked. Apple scrapped the APIs and converted to iCould version 2. Its better, but still not usable, except for the simplest of cases.