I received the following bug when trying to union two parts and was asked by studio to report as a bug. I have also attached a world with the two offending parts I was attempting to union.
Below is the print error studio sent
19:06:28.425 Something went wrong. CSG returned error code -34. Please file a bug report, preferably with a file containing the problematic object(s). - Studio
Hi, thanks for submitting this bug report, including the place file! In this case, the reason it’s failing is because your part “Saloon.003” is a MeshPart, and solid modeling doesn’t accept MeshParts yet, only Parts and PartOperations. It looks like you could use a Part with Shape=Wedge.