Slider duplicate and alt problem

Hello,
In a slider, all the "alt" texts have disappeared. I don't know if you have ever had this problem. I had to redo them on a slider, for 14 images.

Second problem, I can't duplicate the slides. I mean, I have on a slider 14 images and if I want to duplicate a tab, the function is grayed. I tried to delete a tab and I can duplicate again. So I figured it was limited to 14 images... But I have the same problem on another page with a slider that has 17 images...

Thanks for your feedback on these 2 problems.