Check the MBUTTONPAN system variable value, which is used to control the behavior of the third button or wheel on the pointing device.

If the MBUTTONPAN is set to 1—the default value, we can use the middle mouse button to pan and zoom the drawing.

If the value is set to 0, clicking the middle mouse button displays an object snap menu at the crosshairs, as shown in the following picture,

You might be wondering where to get the object snap menu when MBUTTONPAN is set to 1.

Just use Shift+Right-Click