Thumbnail ?

The th folder is only created when the Slider CK is called.
The MediaBox plugin then accesses this folder to display the thumbs - even if the option to create the thumbs is disabled in the MediaBox plugin.
MediaBox Plugin does not create a th folder itself if this is disabled, as mentioned above.
The problem is not necessarily with the MediaBox plugin
If there was an option in the slider module to deactivate the option like in the slideshow plugin, then it might be better.
One possible solution would be: also a different naming of the th folders.
How does the Mediabox plugin know that the th folder is not its folder, but that the folder belongs to the slider module?

(sorry, my english is bad
my French language is even worse)

the problem is not the folder name, this is normal that it uses the same name to avoid multiple thumbs creation
I have just checked by my side and Slider CK does not create any "th" folder nor thumbs
now I'm wondering what is creating this folder on your side

please contact me by email with an admin access :
- remind me the url of this post
- give me the ID of the article/module taht you are editing
- give me the direct url in front to show the module loaded

You're right, the problem has another cause.
Until yesterday I was able to reproduce the error very well. Then I just played around with the JCE mediabox 2 plugin and switched it on and off. Lo and behold - now no more thumbs were created.
 
I can't say for sure whether that was really the case.
It's a private website, I can't give you access.
Nevertheless many thanks. Your support is very good.
The many extensions - I have the full package - are well thought out and functional. This also includes your template creator.
You're doing a good job.

Nevertheless many thanks. Your support is very good.

thank you

for the problem let me know if it comes again