I already have my php memory limit at 256 MB.
Issue of broken woocommerce product editor remains. This issue started not with Cloudflare & WP Rocket I think but when WPML was installed.
Issues with Cloudflare & WP Rocket are already resolved.
I disabled WP Rocket & Cloudflare. And I even changed back to my hosting provider nameservers again.
Every plugin was up to date when issue was found.
I already tried changing htaccess.
In the link to the tip on using cloudflare it states:
"it has been confirmed that minification in CloudFlare can break X Theme 5 and Pro Theme, so be sure to disable them."
Does this also apply to minification settings in cacheing plugins like WP Total cache & WP Rocket?
I think I will restore complete site from backup again.
On the backup everything is working fine. And I'll test on development server first before applying Cloudflare & WP Rocket again...