Drag and drop email in todo sidebar in outlook web doesn't work

I created a shared list in todo and sent the link to my colleagues, they can add task with the "add task" button, but when they drag and drop an email into it, it appears and disappears instantly. I've checked the devtools and it says that the POST request failed returning a 404 error. How is this possibile? Since we can clearly see it and add tasks. 
This started when I've changed a name to a task I've shared, it stopped working (nobody could not add anything) so I've deleted it and from that moment whatever list I've created and shared did not work.