The default route continues to point to "U0" even when all traffic is going through a differen

Symptom:

The default route continues to point to “U0” even when all traffic is going through a different interface.

Condition or Workaround:

Occurs when 3G on “U0” is in manual mode and configured as the primary WAN interface, and “X1” is configured as the alternate WAN for WLB. All traffic passes through the “X1” interface, but it never becomes the active WAN interface or default route.

Resolution or Workaround: 

Upgrading to SonicOS Enhanced 5.6.0.3 release resolves the issue.

Tracking ID: 86747

Source: SonicOS Enhanced 5.6.0.3 Release Notes