The A X B are subtracks. To turn it off, these instructions should help….
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OpenExpanding or collapsing track layers
Right-click the track header and choose Expand Track Layers to expand a video track to reveal three subtracks within the main track: the A roll, B roll, and transition roll. In this view, sequential clips alternate between the A and B rolls, and the overlapping area between events is represented by the transition roll.
Choose the command again to collapse the track layers.
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Best Regards….George