I have the same two "fails" (....mount_unionfs... and ...checkroot-bootclean.sh...) on startup, but the device runs fine anyway.
These boot messages are irrelevant - but also annoying.
I have managed to cleanup the boot messsages in my internal build, except for one boot
message I cannot seem to resolve.
These have no effect on the operation of PilotAware, I have tried to put some debug messages into
the boot log, to indicate when the various interfaces are up and running.
I intend to add these to the webserver interface to indicate success/failure of the interfaces.
Of course if the WiFi fails, then there will be no webserver to indicate the failure!