Boolean Union (Region) fails silently

Having a boolean union fail is fairly common, but now I have a case where I a) can’t see why it is failing and b) it fails completely silently, ie. with no orange node or error message!?

I have a set of flat closed curves that I want to union. This works in 99.9% of cases and now I am curios why it fails here. I have added another example with only 1 less curve and it works as expected.

Any ideas why there is no error message on the Boolean Union node?

boolean-union-region-bug.gh (17.3 KB)