Adding external podcasts via RSS URLs still erattic

I've noticed that on both iOS and macOS, adding RSS URLs to Apple Podcasts has been hit or miss at best. Some will go through right away, while others eventually go through only after multiple attempts. And others still won't go though no matter what, even though those same addresses are easily added using a competing podcast app (in this case, Pocket Casts).

At first, I was quick to blame the podcast provider, but if the same URL can be added elsewhere, then the issue lies with Apple Podcasts. I fail to understand how a company with Apple's resources at their disposal can turn out such buggy apps on occasion.