2021.04.03 update: This issue has been resolved and units can be assigned successfully once again.
We're aware of an issue where SmartMusic throws an error when attempting to assign an entire Unit. This appears to effect both newly-created and preexisting Units.
While the ability to assign Units is currently unavailable, you can still assign individual assignment templates in the meantime.
Our team is actively investigating this issue in order to resolve it and and updates will be posted as comments to this article. Please click Follow to receive email updates when this article is updated.