We’re seeing the same issue: after upgrading to Docker CE version 18.09.2, build 6247962, containers randomly die with exit code 137, OOMKilled flag set to false. No error messages in our application logs, just these entries in /var/log/messages:
containerd: time="2019-03-05T06:14:26.774849684-05:00" level=warning msg="cleaning up after killed shim" id=0a9bc92a6a0e4ec3cb0d3dd535d922f6512f9d22407ed068ec98e496643ec126 namespace=moby
containerd: time="2019-03-05T08:52:07.895620591-05:00" level=warning msg="cleaning up after killed shim" id=778937aeebdc78aacef0cabecc28fb24272e77bc37359e7b5fb8fe120d403b24 namespace=moby