Error: Could not load signature of Zendesk.Repositories.IRequestApiRepository:GetImage

Hi

I am using the Zendesk Mobile SDK for Unity (1.2.5) and I am running into a problem when domain reload happens in the editor (v 2021.1.21f1 on Windows 10) and it fails to load the UnityDLL.dll

Error: Could not load signature of Zendesk.Repositories.IRequestApiRepository:GetImage due to: Could not load file or assembly 'UnityEngine.CoreModule, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. assembly:UnityEngine.CoreModule, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null type:<unknown type> member:(null) signature:<none>

Unloading broken assembly Packages/com.zendesk.support/Runtime/dll/UnityDLL.dll, this assembly can cause crashes in the runtime

This is then followed by a cascading number of errors due to the fact that it cant be loaded.

The only difference between the official plugin and what I've done with it is to create a Package from it by adding two Assembly Defintiion Files to it so that I can load it and use it properly within my project.

More information on that here:
https://docs.unity3d.com/Manual/cus-layout.html

So my question is; why have a dll at all? Can I get the source?