(1) Not sure this is a bug or not, but I'm unable to boolean merge (add) the 2 curves in the attached document. It doesn't work directly and it doesn't work via compound. I simply get an empty result set after an operation (both curves disappear from screen.) For some reason going to the "Layer" menu the "Expand Strokes" option is offered for both curves, even strokes are disabled… feels a bit odd too.
I remember that there was/is some issue with the smart nodes, so I made sure to select all points and convert them to the normal ones ("Smooth"), but this didn't solve the problem either.
(2) Unrelated to the actual boolean failure: if there's some sort of error Affinity Designer should report them (pop up the assistant and let me know the operation failed or something). Basically it just fails silently. In a more complex situation I might entirely miss the problem and then run in problems later when I notice a graphical element is suddenly missing for some reason. Let the user know there was an error.
Bug,1.afdesign