For those I looked into, they are all related to this line of code:
    logging.debug('Post body: %s', self.request.body)

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/a573fb627d6f445089ae59d84da72e178c626dc9

commit a573fb627d6f445089ae59d84da72e178c626dc9
Author: Shuotao Gao <stgao@chromium.org>
Date: Tue Aug 28 23:43:15 2018

[Findit] Fix DeadlineExceededError caused by debug logging.

Bug:  878554 
Change-Id: I68bdae3b73414d7f4fba2b7ae47aca1b2587634d
Reviewed-on: https://chromium-review.googlesource.com/1194897
Reviewed-by: Roberto Carrillo <robertocn@chromium.org>
Commit-Queue: Shuotao Gao <stgao@chromium.org>

[modify] https://crrev.com/a573fb627d6f445089ae59d84da72e178c626dc9/appengine/findit/handlers/completed_build_pubsub_ingestor.py