Build failing on 4 month old tree with no changes even though SOURCE_MIRROR_URL is set

[adrianb]

Tree was building fine when last I touched it - no changes. Today I get this error

WARNING: /home/adrianb/trees/rel_prod/meta-openbmc/yocto/krogoth/poky/../../../meta-aspeed/recipes-kernel/linux/linux-aspeed_4.1.bb: Exception during build_dependencies for do_patch
WARNING: /home/adrianb/trees/rel_prod/meta-openbmc/yocto/krogoth/poky/../../../meta-aspeed/recipes-kernel/linux/linux-aspeed_4.1.bb: Error during finalise of /home/adrianb/trees/rel_prod/meta-openbmc/yocto/krogoth/poky/../../../meta-aspeed/recipes-kernel/linux/linux-aspeed_4.1.bb
ERROR: ExpansionError during parsing /home/adrianb/trees/rel_prod/meta-openbmc/yocto/krogoth/poky/../../../meta-aspeed/recipes-kernel/linux/linux-aspeed_4.1.bb: Failure expanding variable do_patch, expression was cd /home/adrianb/trees/rel_prod/meta-openbmc/build/tmp/work-shared/wedge100/kernel-source

# executes and modifies the source tree as required
patchme wedge100
if [ $? -ne 0 ]; then
	bberror "Could not apply patches for wedge100."
	bbfatal_log "Patch failures can be resolved in the linux source directory /home/adrianb/trees/rel_prod/meta-openbmc/build/tmp/work-shared/wedge100/kernel-source)"
fi

# check to see if the specified SRCREV is reachable from the final branch.
# if it wasn't something wrong has happened, and we should error.
machine_srcrev="${SRCREV_machine}"
if [ -z "${machine_srcrev}" ]; then
	# fallback to SRCREV if a non machine_meta tree is being built
	machine_srcrev="AUTOINC"
	# if SRCREV cannot be reached something is wrong.
	if [ -z "${machine_srcrev}" ]; then
		bbfatal "Neither SRCREV_machine or SRCREV was specified!"
	fi
fi

    if [ -n "yes" ]; then
        current_branch=`git rev-parse --abbrev-ref HEAD`
        machine_branch="${@ get_machine_branch(d, "master" )}"
        if [ "${current_branch}" != "${machine_branch}" ]; then
            bbwarn "After meta data application, the kernel tree branch is ${current_branch}."
            bbwarn "The SRC_URI specified branch ${machine_branch}."
            bbwarn ""
            bbwarn "The branch will be forced to ${machine_branch}, but this means the board meta data"
            bbwarn "(.scc files) do not match the SRC_URI specification."
            bbwarn ""
            bbwarn "The meta data and branch ${machine_branch} should be inspected to ensure the proper"
            bbwarn "kernel is being built."
            git checkout -f ${machine_branch}
        fi
    fi

if [ "${machine_srcrev}" != "AUTOINC" ]; then
	if ! [ "$(git rev-parse --verify ${machine_srcrev}~0)" = "$(git merge-base ${machine_srcrev} HEAD)" ]; then
		bberror "SRCREV ${machine_srcrev} was specified, but is not reachable"
		bbfatal "Check the BSP description for incorrect branch selection, or other errors."
	fi
fi

which triggered exception FetchError: Fetcher failure: Fetch command failed with exit code 128, output:
fatal: unable to access 'https://github.com/theopolis/linux.git/': Failed to connect to github.com port 443: No route to host

Summary: There were 2 WARNING messages shown.
Summary: There was 1 ERROR message shown, returning a non-zero exit code.
CL-Ubuntu15:~/.../meta-openbmc/build$