The latest release of Woocommerce ( 8.5.1 ) has caused a number of sites to receive a critical error, if they have a particular configuration. Namely it involves those who's hosting packages use ModSecurity so it's not limited to one company and covers a number of the top hosting platforms such as Plesk and cPanel.
In addition your Woocommerce would need to have the Order Attribution feature enabled and the combination of the 2 causes a critical error on the website.
Here is a link to the issue with some of the mitigations but, as with any updates, you should follow these simple principles so you protect your website from going down.
1. Always take a backup of the site, prior to carrying out any updates.
2. Create a staging site to carry out the backups on first and check if any problems occur.
3. Ask an expert to do the updates or take out a maintenance and support package to save you the worry!
If you have experienced issues with your Woocommerce upgrade or would like support with maintaining your Wordpress website then please get in touch.