Not the sequence list itself, but the images inside each sequence are not sorted. So, in the Upload tab I open a sequence, and get thumbnails of all images in this sequence. These are often not sorted.
I had to use an external host for the image, the Mapillary forum no longer lets me upload images. 
Maybe I need to provide a reason why I want sorted images.
I am capturing while walking or cycling, and this often means I have to start capturing before mounting my phone. This means the first and last images of each sequence are showing my hands, my feet, my face, etc. So I want to clean up sequences before I upload them, by removing the first and last few images.
And this becomes extremely difficult when those first and last images are spread out somewhere in the middle of the thumbnail list.