Why you might be getting the error "Mismatching Versions" when installing/upgrading Q-assign
This error occurs when you try to install the latest version of an app (Q-assign) onto an instance that hasn't been updated to the newest Salesforce release yet. This is an expected behavior.
Note: Salesforce Sandboxes instances will not stay with same as Production. If your Sandbox is on a different instance which is upgraded to the latest version you should be able to install Q-assign on that Sandbox.
You can find information on which instance have been updated on Salesforce Status website: https://status.salesforce.com/status
Please contact firstname.lastname@example.org for any questions.