While I haven't got a simple example, by this time I am sure the issue is not in my code. (it's not online avail yet)

I have a class, with 2 corba interfaces

  TIdeLocalsValue = class(TLocalsValue, TWatchAbleResultIntf, TWatchAbleDataIntf)
...
end

If I get an interface using
  (SomeVar as TWatchAbleDataIntf).Foo

it either crashes, or calls the wrong method.

If I swap the order of the interfaces in the declaration, then it works (but the other interface will fail).

And yes, the object on which I work is of the correct class. And it is alive (not a dangling pointer).

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I have  tried to introduce a Base class, and move one Interface to that base class, but no luck ....

So it seems to be that topic
https://forum.lazarus.freepascal.org/index.php?topic=39416.0

> Is and As operators require that the interface has a GUID defined

Only that in my case the compiler happily compile

(MyObjec as TCorbaWithoutGUID).foo;

Shouldn't that give an error?