Hi Chromer, This error usually happens when Salesforce doesn't allow changes to the current agent version. 

Try these steps:

1. Check if the agent is active. Deactivate it before making changes.
2. Refresh Agent Builder and try publishing again.
3. Check if any deployment or publishing process is still running.
4. If possible, try creating the agent again in a fresh Trailhead org.
5. If the issue continues, raise a Trailhead support case with the error and request ID.

It could also be a temporary Salesforce platform issue.

Hope this helps!