Cannot add new Project Slides in Product Portfolio page

Dear Support,

We have a website running Inovado 4.6.6 theme on WordPress 4.9.4.

When we click on the “select files” or drag & drop a picture to the “drop image files here” section, nothing happens, no error message, no confirmation.

See screenshot where we try this:

We have tried different browsers, and also enabled the debug option in wordpress, but no error message is logged.

Any way we can solve this?

Best regards,
Ro

Ticket