[SOLVED] Wordpress 5.0.x shows blank pages / posts in classic editor

Non-technical end users have been trained to adds posts to the site, so there is no desire to change things up and use the block editor. Classic editor is installed and set up as default, and users can not switch to the block editor.

Site is https://harrisonresearchlabs.com/

Since the client does the updates, not exactly sure which version of release 5 initially broke the site, but problem was that the all the posts and pages were showing up blank in the editor in 5.0.3, both the text and the visual, even though the front end rendered fine.
Rolling back to 5.02 allowed you to edit in the text tab, but the visual tab still blank.

referring to this article https://www.wpbeginner.com/wp-tutori...visual-editor/

I added the following line at the very top after the php opening tag in the config file.


define('CONCATENATE_SCRIPTS', false)

Site is working now, but looking for a way to make this line of code persistent...in other words, how can I make it survive WP updates without adding it back each time?