Hello, thank you for getting in touch and for your support!
It seems that it might be caused by a conflicting identical class name without a namespace specific to your project, it is always good practice for classes to be declared inside a proper namespace to ensure this issue doesn't happen with other plugins.
Just in case, I've tested the latest ASE version with Unity's Substance plugin and everything is compiling as expected.
I would suggest that you first delete the ASE folder and reopen Unity, then check if there are any errors present in the project, as these might interfere with the package importer. Then, after resolving any errors present,
download the latest ASE version from our website and extract it into your project.
If the issue persists, either use Visual Studio to locate where the conflict is or using a new project with only ASE installed import your current project's packages one by one until the culprit is found.