for WP7608, you need to use R16.1:
https://source.sierrawireless.com/resources/airprime/software/wp76xx/wp76xx-firmware-release-16,-d-,1/#sthash.IXqI8wz7.G9fcfjET.dpbs
And you need to use swi-wp76_5.0.5 which is for (Release 16.1 + Legato 19.11.6)
Or you can use R16.3:
https://source.sierrawireless.com/resources/airprime/software/wp76xx/wp76xx-firmware-release-16,-d-,3/#sthash.hA41yzsv.dpbs
swi-wp76_5.0.6 is for (Release 16.3 + Legato 19.11.6)