I think it is by design. If you like performance condition visible, you may add a data field to the display. It's under "Other fields"
Performance Condition should pop-up after 6 minutes of running using the native Run app with valid data for HR and pace. Note that it might take longer if the data input isn't good/stable enough for the algorithms to give a result. (same as for VO2max)
If you want to monitor PC on the watch throughout your run, you would need to add it as a data field as DmitryB says, however you don't need that in order to get the 6 minute notification or to record PC to the activity for review later.
I believe it's only the apps that has VO2max estimation that will give PC, which for running means only the native Run app.
Which app are you using when the notifications are missing out?