Summary

The project timeline shows all the sprints mixed together and can't set the sprint to the issue using drag & drop.

Environment

Jira Cloud

Cause

This behaviour is seen when you have a specific sprint with long dates((g: 3, 9 months) that overlap with the other sprint's dates.

Solution

There are two possible workarounds:

1. Please check the sprint dates which have long dates and adjust the dates. Then, you can set the sprint to the issue using drag & drop in the timeline view. Please refer to the below screen-recording.
   
2. In case the dates are intentional, you won't be able to assign issues to the sprint via drag-and-drop. However, you can use the right-click menu to update the sprint.