When the session is started with the hardware decoding disabled, and the user enables it later, the NoMachine client becomes unresponsive and needs to be terminated via Task Manager. This behaviour is not always reproducible.

As a workaround, launch the client program, connect again to the server and disable the hardware decoding for that session.

This setting is available in the NoMachine menu -> Display -> Change settings -> 'Modify the advanced options' -> 'Advanced display settings panel'. To open the NoMachine menu, ctrl+alt+0 or click on the page peel in the top right corner of the window.