Symptoms
SharePoint worklist webpart stucked in loading mode in IE 11 with Blackpearl 4.6.8

Diagnoses
This issue only persistent in IE 11 only

Resolution
This issue only exists in IE 11 and this browser version do not fall under supported matrix of Blackpearl 4.6.8 (http://help.k2.com/blackpearl/support-matrix). There are 3 options on this:-
1) Upgrade to Blackpearl 4.6.9 which is supporting IE 11, or
2) Set the IE to run in IE 10 mode or use other browsers such as Chrome, or
3) Force the IE to run in IE 10 mode by specify HTTP Header in runtime site web.config as outlined in https://www.modern.ie/en-us/performance/how-to-use-x-ua-compatible.