Steps:

• unpack and open attached Cluster.zip project in VS Code
• set breakpoint in test.js line 15
• start debugging by running the "Cluster" launch config
• after hitting breakpoint press Continue button on debug toolbar

Observe: a new debug session starts and the corresponding node in the CALL STACK gets selected. As a consequence the debug focus switches to the new session and the debug toolbar no longer shows the "Continue" button. In order to continue stepping, a stopped debug session must be selected in the CALL STACK view.
This happens for every new child process of the cluster...

A new debug session should never change the selected session in the CALL STACK view (at least if there is already a stopped debug session.