Hi @RueNel,
Thanks for your input you make me feel comfortable in these situations.
Now I have done it again. Same outcome as before when I started this thread. I have also tried to do the same as I did when I solved it but this time: no cigar.
I do not understand what I am doing wrong, I’m tweaking with W3TC and everything works great with the website and the Essential Grid works great until I’m about to edit the pictures. It will not load the JS in the WordPress interface.
I have tried to deactivate the plugins and tried the older backup before I started tweaking but its still the same outcome. Now I’ve reached a dead end and as I can see I still have 2 cs-body.js in my file manager:
wp-content/plugins/cornerstone/assets/dist/js/site/cs-body.js
wp-content/updraft/plugins-old/cornerstone/assets/dist/js/site/cs-body.js
Can someone explain to me why this happends? I guess it has something to do with W3TC.
F.Y.I.
When I go into the both cs-body.js I can see the following warning (see attachment) 
I Can see that it has generated old folders and old-old folders into my filemanager and alot of the JS scripts now contains errors like the attached picture.
I really have to tweak my website and I would love to get an answer of what I should not touch the next time…
Thanks in advance.
Best regards