As a counter-example, I haven't had an entirely successful Google Takeout export in at least a couple of years, using their service to schedule the exports automatically every two months.

I always have a failure with Google Fit data, which reports 'Service failed to retrieve this item' on the same JSON file every time. I assume this is something corrupted at their end.

It's not that uncommon for my exports to intermittently show failures with other services -- for example, my latest export, taken on April 20th, also failed to include one of my YouTube videos, with the same 'Service failed to retrieve this item' error. That video is usually included successfully, so I'm guessing this was a glitch.

Nothing major, but I can well believe that others also experience regular errors, although I'm sure we're in the minority.

It's been about a year since my last round (so it is probably time to do another backup) but there were a few services that were flaky. It wasn't even me auditing for missing data, the takeout page would notify you that some data failed to be packaged up.

Combined or not, google keep notes without titles always get failed or errors in takeout html.