Reproduction steps:
1. Open attached project.
2. Open "1" scene.
3. Select "Main Camera" game object and expand attached "Test Scene GUI" component.
4. Click and hold the right mouse button on the scene view.
5. Drag mouse on to the button in the left upper corner of the scene view.
6. Click this button with the left mouse button while still holding the right mouse button.
7. Scene view and scene manipulation tools becomes unresponsive(GIF attached).

Note:
* play and stop the scene to reset this issue.