I maintain a Shopify API package for .NET [0] and this has largely been my experience as well. Their attitude toward breaking API changes has caused me a good deal of frustration in the past. To make matters worse, their docs weren't (and still aren't, in my opinion) that great; my biggest complaint being they typically don't document when values can be null or even have a different type (e.g. property X could be a string or a decimal, but you'll never know looking at their docs).

This has led me to taking the drastic step of making _every_ property nullable. It's gross and feels bad to use, but at least it prevents JSON parse operations from crashing applications when a value is unexpectedly null.

[0]: https://github.com/nozzlegear/shopifysharp