juniorm on "[Plugin: WP Super Cache] Super Cache and "headers already sent" php error"

After updated, there is an issue about "headers already sent". I did nothing but added a simple function to an existing php file on my theme folder. This function does not print /display anything. So after the blank pages, I had to delete cache folder, delete the WP Super Cache plugin folder to get my site back to work. Some people are saying this problem is due to a blank space between ?> <?php
but this is not the case since I cannot find it in my code, I will dig Super Cache source code to check if I can find something strange.

https://wordpress.org/plugins/wp-super-cache/