When pages look messed up, broken, or seem to have lost their styling (everything is no longer in columns), it's usually because your e-commerce provider's editor has overridden the Shogun page.
There isn't parity between the two editors, so any edit made in one overrides the other. This can even be a very small edit like changing a meta description.
How to fix a page with broken stylings
The fix is easy: go into Shogun and make a very small change to the "broken" page (like adding a space somewhere), and republish it.
It should be all fixed at that point.
How can I prevent the page from breaking when editing outside of Shogun?
Disabling WYSIWYG mode in your BigCommerce store settings is the easiest way to do this, this turns the input box in BigCommerce into a plain text box that will not strip out Shogun content from your page. You can follow the steps below for more information on how to disable this:
Go to Store Setup
Go to Store Settings
Go to Display
Navigate to Control Panel