When customizing dashboard widgets in the Platform, you may want to delete some widgets by clicking the Delete button ('cross' icon) in the upper-right of the widgets. That looks successful as you don't encounter any error message, but when you reload the Dashboard, some of the deleted widgets appear.
This issue occurs because you cannot delete the generic widgets in the Platform.
Our engineers are aware of the issue and we will endeavor to fix the problem in a future release.
Unfortunately, there are no possible workarounds that you can perform for this problem at this time. So if you encounter this issue, please contact our Support Services team who will be happy to help resolve the issue for you.