What could be a cause for corrupted SCO audio on some smartphones using the Sterling LWB5+ BT radio?

Please check if you have 2EV5, 3EV5 3EV3 frames enabled your in mSBC decoder settings.

Even though it might say those frames are supported, they are actually not.

When send 'Accept Synchronous Connection Request ' set
3-EV5 may NOT be used 1
2-EV5 may NOT be used 1
3-EV3 may NOT be used 1

2EV5, 3EV5 3EV3 frames are not supported in mSBC decoder.