Hey, Jamie and Nick!
Karlie here from the Shopify Guru Team! I am so sorry to hear that you are experiencing this downtime with your site. However, I would be happy to help guide you in the right direction here with a workaround.
Your first step in situations like these would be to get in contact with your internet service provider and let them know that you are having issues accessing your Shopify site with IP 18.104.22.168. Your internet service provider may be able to fix this issue for you, but if it is a work in progress - then you can follow the following steps to switch to Google's DNS settings.
Switching to Google's DNS settings should help to get your storefront back online. If you do switch over to Google's DNS settings - then you can then switch back after your internet service provider has fully resolved the issue for you. To configure your network settings to use Google Public DNS you would want to follow the step by step Google guide here. When adjusting your settings, make sure that you switch to the 'IPv4' option, which will look like this!
I hope this helps, but if you have any further questions - be sure to ask and I would be happy to help!