Symptoms

Batch action does not work when all items are selected. It just shows generic "Page cannot be found" in pop up window. At the same time single item action or batch action on all but one items work with no issues.
 

Diagnoses

This is a known issue which appears in certain scenarios when batch action on one of the process activities works with errors if all check boxes are selected. This issue has been logged internally for further investigation.

Reproductions steps:
1. Create a managed path site that does not have a root site
2. On the worklist webpart - click "Select all" button
3. Select a batch action
If you have a root site you won't see the error because the page exist

Workarounds:
1) After clicking the select all tick box. Un-select one work-list item and re-select it.
2) Create a root site and activate the K2 components on it.

Note that according to MSFT documentation you have to have root site collection - otherwise it means unsupported state, without a root site collection many things break, like InfoPath, Workflows, Visio services as these all expect the root site collection to exist.
Please refer to Microsoft KB which says that "Any web application which does not have a site collection and web provisioned at the root (/) is not supported unless every site collection is a host header site collection in the web application":
https://support.microsoft.com/en-us/kb/2590564
 

Resolution

This is known issue with available workarounds. See workarounds in Diagnosis section.