All audio tracks greyed out, although normally playing

As it happens sometimes, I solved the problem by restarting FCP after deleting preferences. Obvious right? Not really. I did that earlier a few times, but without success. Hence my question on this forum. Trying later on again, it worked, automagically. Of course I have no explanation for this lagging resetting of FCP.

BTW, I wish that this "delete the preferences"- stuff would go for good. Could you imagine people doing that on their iPad or phone? I know... make a suggestion etc...