Do these errors only occur when starting a build from inside Visual Studio and not when building in Unity (both when scripts are compiled automatically upon any change, and when building your executable)?
I assume you have already tried what can be seen in this forum posting, as Misaki mentioned here to you on this other thread:
I just found a potential reason for this type of problem: when using an older Visual Studio Editor package in the Unity Package Manager, an issue as described by your posting can be reproduced. Could you please have a try upgrading the Visual Studio Editor package via the Unity Package Manager and then hit Assets - Open C# Project?
If all of the above did not resolve your issue, how are you importing the spine-unity runtime? If you are using the Unity Package Manager, please have a try removing and re-adding the spine-unity packages, in order spine-csharp before spine-unity.
