Prestashop I can't upload product images from backend

I can't upload product images from backend, always the last image is incomplete and doesn't upload, no matter if is a single image o are multiples images, the progress bar is freeze.

I deleted the cache, I activated the debug mode, I checked the php_error.log and prod.log, dev.log in the prestashop installation and I can't see any error there. Well, I only can to see an Ajax error in debug mode and browser console, a POST petition without status response (see attachments). How I Can debug this?

The images are very small < 500kb.

What setting or log I must to check?

My current settings are:

• OS: Ubuntu 18.04.2
• Prestashop: 1.7.5.2
• Folders Permissions: 755
• Files Permissions: 644
• PHP: 7.1
  • memory_limit = 1024M
  • max_execution_time = 300
  • max_input_time = 300
  • upload_max_filesize = 20M
  • post_max_size = 20M
  • max_input_vars = 10000
  • safe_mode = off
• Browsers: Chrome, Firefox, Opera.

I checked the modules installed that could affect the product backend area and I found [Free Module] Image Optimization Via Resmush.it Service.

When I deactivated this module the product images uploads works fine. Now, I must check what is the cause of the issue into this module.