Split: URGENT – the_content error on editing HTML BLOCK

Hi, thanks for find the cause of the problem.
The solution works.
I just have a doubt. The plugin comes with the site and this is the reason why I didn’t deactivate it to test. I’m not so technical skilled to identify the function of this plugin (I tried understand here: https://narrateworld.supergap.it/wp-admin/plugin-install.php?tab=plugin-information&plugin=redux-framework&TB_iframe=true&width=600&height=550), but I suppose that if you add this plugin in the native ones of Woodmart (WP mantra is to install as less plugin as possible), must be a reason why. Which is the feature/performance/settings/ability I loose without this plugin?
And just to know, how can it generate a so big issue suddenly, without other site changes or other plugin upgrading. I see hat there is an upgrade for this plugin. Is that an alternative solution instead deactivating it?
Thanks for the patience for all these questions, but as you can image, I fear for the wealth of the site, in the short and long period.
Regards, Giorgio.