Sometimes, when you press the spacebar, the play button changes to pause, but the Premiere Pro screen doesn't actually start playing.
This may be due to the current playback setting in Cutback.
Check the playback location. Click the three dots next to the play button in the [Rough Cut] preview. You can choose between “Cutback” and “Premiere Pro.”
Make sure it's set to the location you want to use.
If it's set to Premiere Pro, try setting custom In/Out points in your sequence and then play again. (In Premiere Pro sequence, move the playhead to the section you want, then press I and O to set In and Out points.)