I had this problem for the first time today. Last night I was working on the same project and all was normal. Today I booted my DAW and opened the project to find no sound. Turning off the read automation followed by clicking on the fader restored the sound (like others, even when read was engaged clicking & holding on the fader caused it to play until the mouse was released). Didn’t need the automation for the day’s task so I left it off and haven’t explored the problem further. However a project that was working fine yesterday wasn’t today. Between then and now no changes were made to the OS, no software was installed or uninstalled (including drivers), no hardware was changed - everything is exactly like it was last night. The only thing that happened was that I shut the system down last night and restarted it this morning.
At the moment I don’t need automation, but will soon
EDIT:
Closed my current project and loaded several different projects that I knew had automation, some recent some older. None of them produced sound. Shutdown Cubase, and restarted it. Now all those same projects play fine (knock on wood).