seo – Why Google could canonize between the pages of hreflang?

As far as I know, one of the most important use cases, and basically all the hreflang point is to be able to control which domain should classify where, when it is not obvious.

I realize that, from time to time, Google ignores and overwrites my own canonical reference and canonizes one cctld page to another (for example, .de a .at).

This does not seem to make any sense. How can I push google to do it the right way? Are the canons referring to themselves confusing google?