Any CPU DLL does not work in 64 bit editor

Hi everyone,

I have this .dll written in C# from a third-party. (trial available here)

It is supposed to be built for "Any CPU" architecture. It works fine in the Unity 32-bit Editor, but the 64-bit Editor crashes right away, with no helpful information, and the whole editor exits. The Windows eventviewer reports it as a heap corruption, which is far beyond my debugging skills. The editor.log reports no errors.

The fun part is, if I make an C# application (so no Unity involved) with this DLL, compiling and running as both 32-bit and 64-bit works just fine. This makes me think the problem lies in Unity, because this proves the DLL is indeed suitable for "Any CPU", not just 32-bit.

I have tried setting all possible combinations in the platform settings of the DLL, but to no avail.

Since the editor seems to crash on a single method-call, I suspect the DLL uses some reference that is buggy when used with mono. However, I have no clue how to check.

Can someone push me in the right way as how to solve this?