Issue when sort the gallery field from frontend

Hello

I’m trying to sort the image gallery from my edit post but sometimes works and sometimes doesn’t work.

I added 3 images and then I set a caption for each image: Hello 1, Hello 2, Hello 3.

Then I move the image with Hello 3 caption in the first position and Save the post.

When I see the post saved, Hello 1 hasn’t a caption, Hello 2 has a new caption “Hello 3“ and  Hello 3 has a new caption “Hello 1”.

Additionally, the sort doesn’t effect.

Thanks for your help