[ADD relevant info inline]
Octopus and Kalista factory builders failed to build since Jan 10 2019

Link to build or pfq page.
https://uberchromegw.corp.google.com/i/chromeos.branch/builders/octopus%20factory%20factory-octopus-11512.B
https://uberchromegw.corp.google.com/i/chromeos.branch/builders/kalista%20factory%20factory-nami-10715.B

build # for that buildbot.
https://uberchromegw.corp.google.com/i/chromeos.branch/builders/octopus%20factory%20factory-octopus-11512.B/builds/1
https://uberchromegw.corp.google.com/i/chromeos.branch/builders/kalista%20factory%20factory-nami-10715.B/builds/33

Snippet of log that contains the failure.
tools_internal (ERROR)
----------------------------------------
[0:00:12] Started.
[0:00:13] running "git cat-file -e 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce^{commit}" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] fatal: Not a valid object name 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce^{commit}
[0:00:13] /b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps has 2 .pack files, re-bootstrapping if >50
[0:00:13] running "git config gc.autodetach 0" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] running "git config gc.autopacklimit 0" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] running "git config core.deltaBaseCacheLimit 2g" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] running "git config remote.origin.url https://chrome-internal.googlesource.com/a/chrome/tools/build/internal.DEPS.git" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] running "git config --replace-all remote.origin.fetch +refs/heads/*:refs/heads/* \+refs/heads/\*:.*" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:13] Fetching +refs/heads/*:refs/heads/*
[0:00:13] running "git fetch origin +refs/heads/*:refs/heads/*" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:14] From https://chrome-internal.googlesource.com/a/chrome/tools/build/internal.DEPS
[0:00:14]  * [new branch]      chromium/3668 -> chromium/3668
[0:00:14] fetch +refs/heads/*:refs/heads/* took 0.0 minutes
[0:00:14] Fetching +refs/tags/*:refs/tags/*
[0:00:14] running "git fetch origin +refs/tags/*:refs/tags/*" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:14] fetch +refs/tags/*:refs/tags/* took 0.0 minutes
[0:00:14] Fetching +refs/branch-heads/*:refs/branch-heads/*
[0:00:14] running "git fetch origin +refs/branch-heads/*:refs/branch-heads/*" in "/b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps"
[0:00:15] fetch +refs/branch-heads/*:refs/branch-heads/* took 0.0 minutes
[0:00:15] From /b/git-cache/chrome--internal.googlesource.com-a-chrome-tools-build-internal.deps
[0:00:15]  * [new branch]      chromium/3668 -> origin/chromium/3668
[0:00:15] _____ tools_internal : Attempting rebase onto 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce...
[0:00:15] 
[0:00:15] Rebase produced error output:
fatal: Needed a single revision
Does not point to a valid commit: 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce
----------------------------------------
Error: 7> Unrecognized error, please merge or rebase manually.

....

Error: Command 'git checkout --quiet 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce' returned non-zero exit status 128 in /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal/tools_internal
fatal: reference is not a tree: 7f3f19539cdd5bfc2ccdabdac38ef721d408ffce



Warnings:
Conflicting directory /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal/tools_internal deleted.
Conflicting directory /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal/src-internal deleted.
sync_chrome: Unhandled exception:
Traceback (most recent call last):
  File "/b/c/cbuild/repository/chromite/bin/sync_chrome", line 169, in <module>
    DoMain()
  File "/b/c/cbuild/repository/chromite/bin/sync_chrome", line 165, in DoMain
    commandline.ScriptWrapperMain(FindTarget)
  File "/b/c/cbuild/repository/chromite/lib/commandline.py", line 912, in ScriptWrapperMain
    ret = target(argv[1:])
  File "/b/c/cbuild/repository/chromite/scripts/sync_chrome.py", line 76, in main
    SyncChrome(gclient_path, options)
  File "/b/c/cbuild/repository/chromite/scripts/sync_chrome.py", line 52, in SyncChrome
    ignore_locks=options.ignore_locks)
  File "/b/c/cbuild/repository/chromite/lib/gclient.py", line 262, in Sync
    return cros_build_lib.RunCommand(cmd, cwd=cwd, **run_args)
  File "/b/c/cbuild/repository/chromite/lib/cros_build_lib.py", line 646, in RunCommand
    raise RunCommandError(msg, cmd_result)
chromite.lib.cros_build_lib.RunCommandError: return code: 1; command: /b/c/cbuild/repository/chromium/tools/depot_tools/gclient sync --with_branch_heads --with_tags --reset --force --delete_unversioned_trees --nohooks --verbose --ignore_locks
cmd=['/b/c/cbuild/repository/chromium/tools/depot_tools/gclient', 'sync', '--with_branch_heads', '--with_tags', '--reset', '--force', '--delete_unversioned_trees', '--nohooks', '--verbose', '--ignore_locks'], cwd=/b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal
21:23:58: WARNING: Command failed with retriable error.
return code: 1; command: /b/c/cbuild/repository/chromite/bin/sync_chrome --reset --ignore_locks --internal --tag 73.0.3654.0 /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal
cmd=['/b/c/cbuild/repository/chromite/bin/sync_chrome', '--reset', '--ignore_locks', '--internal', '--tag', '73.0.3654.0', '/b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal'], cwd=/b/c/cbuild/repository
21:23:58: INFO: RunCommand: /b/c/cbuild/repository/chromite/bin/sync_chrome --reset --ignore_locks --internal --tag 73.0.3654.0 /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal in /b/c/cbuild/repository
21:23:58: INFO: RunCommand: /b/c/cbuild/repository/chromium/tools/depot_tools/gclient revert --nohooks in /b/c/cbuild/repository/.cache/distfiles/target-factory-octopus-11512.B/chrome-src-internal