We are seeing the same problem after this latest plugin update to version 2.1.6. It seems that after the update there are some issues caused by this Mailchimp for Woocommerce plugin. The issues we are seeing is that trying to save any settings for themes or other plugins is not working and also changing plugins active/inactive doesn’t work in the backend. Also trying to use any CLI commands gives the error Shane mentioned: Error: Callable “Queue_Command” does not exist, and cannot be registered as wp queue
Only way to deactivate the Mailchimp plugin was changing the name of that plugins folder. After deactivating this plugin everything started working again. WordPress doesn’t seem to allow reactivate the Mailchimp plugin (I did change the plugin’s folder name back to original). If trying to activate it from the backend it doesn’t stay enabled and trying the activation from CLI gives the previously mentioned “Queue_Command” error.
I wonder if these errors are somehow related to the options autoload feature introduced in this version of the plugin. But clearly this should be fixed. Until then I think I’ll revert back to the previous version or just keep the plugin disabled.