Currently the icon URLs on the dashboard that come from the avatar-cache are broken, since they are prepended by a slash . This occurs when using project folders with Bitbucket branch source plugin. Downgrading Jenkins to 2.334 fixes this issue.
I think it was introduced with Pull 6273.
For example the icon URLs look like the following:
|Field||Original Value||New Value|
|Remote Link||This issue links to "Pull 6273 (Web Link)" [ 27412 ]|
|Remote Link||This issue links to "Downstream issue Bitbucket source plugin (Web Link)" [ 27413 ]|
|Resolution||Duplicate [ 3 ]|
|Status||Open [ 1 ]||Closed [ 6 ]|