I and quite a few others ran into some issues with Booster for WooCommerce.
wp_mail has been declared by another process or plugin.
Upon submitting a support request as a paying customer, there was no response for over four days. However, looking at the free plugin support forum, it seems this isn’t the only issue with the new update. Many other people were having problems with the new plugin update. The latest update seems to have addressed the issue.