Hi,
Regarding the “fastboot mode”, it has been disabled for WP85 modules since Legato 16.01 delivery.
It is listed in the Customer Release Note available on the “Source”:
But it should come back in the future delivery.
If you were using fastboot tool for flashing Yocto images then you can still use fwupdate tool to do the same (using *.cwe files generated in the build folder).
Jay