Another very common issue in Magento 2 are white pages in back end, error that I resolved was related to Credit Memo functionality but similar method can be applied to similar issues as well.
To describe issue a bit more, I went to Sales > Order Management > Orders and selected order that should be refunded. Issue was found on several orders and they were made using Authorize.net or PayPal payment), so I excluded possibility that custom payment method could cause issue.
In order screen I clicked Credit Memo button and landed on white page without any error message or notification. Since there were no errors in browser console (wanted to check for java script errors), I checked var/log/systemlog file and found error log:
main.CRITICAL: Broken reference: No element found with ID ‘before.body.end’.
After checking few topics about issue and suggested solutions I decided to try simplest one, to update XML file and add missing layout parameter.
For the sake of test I deiced to edit core file at line #8:
and changed original code:
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">