The autocomputed value of a computed field is displayed with a different precision depending if the rendering of the information is done on the backend side or on the frontend side via the value retrieved via the REST API.

One possible way to see the issue is to created a user story with 2 tasks with one having a 0.1 remaining effort and the other 0.2. In the tracker artifact view, the user story will have a 0.3 remaining effort, on kanban cards or elsewhere you will see 0.30000000000000004.

This is not unexpected but the display should be coherent.