Great to hear that option is already checked.
Sorry, I should have been more clear on cache services. Most hosting providers provide cache services by default as part of their hosting plans. We’d also recommend syncing with your hosting provider to understand how or if those are being used.
One other recommendation would be to perform a theme/plugin conflict test, as outlined here to try and identify if a conflict is occurring. To perform the test, change to the default Storefront theme and deactivate all other plugins with the exception of WooCommerce and Order Hours Scheduler. Check if the issue still continues, if no, activate one plugin at a time until the issue occurs again to isolate the conflict.
The last item to check is your logs, located in the Status setting of WooCommerce at,/wp-admin/admin.php?page=wc-status&tab=logs check for any logs generated with zhours. If you find any error logs with zhours, please send them to us to review and troubleshoot.
I hope this additional information is helpful.