According to Chan's observation, there might be many more such case.

Just verified the query ran fine, so passing over to Chan to investigate at the service side.

Based on logpoints, the possible issue is related to https://pantheon.corp.google.com/errors/CPihicHorbvreQ?time=P1D&project=findit-for-me

Trace back:
at GetLogFromViewUrl (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/infra_api_clients/logdog_util.py:241)
at GetStepLogForLuciBuild (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/services/step_util.py:386)
at GetWaterfallBuildStepLog (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/services/step_util.py:427)
at GetStepMetadata (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/services/step_util.py:444)
at Wrapped (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/libs/cache_decorator.py:188)
at GetIsolateTargetName (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/services/step_util.py:474)
at NormalizeStepName (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/model/flake/flake.py:168)
at _CreateFlakeFromRow (/base/data/home/apps/s~findit-for-me/flake-detection-backend:19344-5326ba9.414431190448041955/services/flake_detection/detect_flake_occurrences.py:81)

I found that there's no step_metadata for some steps for example see chrome_junit_tests 
 in https://ci.chromium.org/p/chromium/builders/luci.chromium.try/android-kitkat-arm-rel/139308 and suspect that's the root. And when I implemented the logic of getting step_metadata, I made a wrong assumption that all test steps have that data.

I have a small change at Findit side and hopefully this can help us resume storing retry with patch flakes.

Then I'll look into adding step_metadata to steps like chrome_junit_tests 

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/24aba6c6bf38bbe5e5d122c00bf11f066c0c3cdd

commit 24aba6c6bf38bbe5e5d122c00bf11f066c0c3cdd
Author: Chan <chanli@chromium.org>
Date: Wed Dec 05 17:35:01 2018

[Findit] Add check on the existence of view_url for a log.

Bug:  911830 
Change-Id: I0c35b84a94699065f1403245b0243d1bc84fc1a2
Reviewed-on: https://chromium-review.googlesource.com/c/1362523
Commit-Queue: Chan Li <chanli@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#19361}
[modify] https://crrev.com/24aba6c6bf38bbe5e5d122c00bf11f066c0c3cdd/appengine/findit/services/step_util.py
[modify] https://crrev.com/24aba6c6bf38bbe5e5d122c00bf11f066c0c3cdd/appengine/findit/services/test/step_util_test.py

Findit is back to normal