I did some furthers tests on this topic.
This problem also occurs in macros.
It seems the main problem is, that the default values for custom objects / attribute isn’t set anymore.
yes, this change is actually (now) working as expected (at least the required part and validation error you get). The issue ( https://github.com/zammad/zammad/issues/1259 ) earlier was, that after ticket creation Zammad ignored mandatory fields. So frankly, you could simply unset their values without Zammad to stop you from doing so.
With Zammad 3.0 we improved this.
This however will force anything that updates tickets to setthe required fields to any value (if it’s not already set.
As for “my default values are not set” - this seems like a bug, if you’d please fill a bug report on Github, I’d really grateful.