Thanks T1mb3, September fix worked great for me. I don't ever wipe cache.
Step by step directions to flash monthly update:
Current support URL -
https://xdaforums.com/nexus-5x/general/nexus-5x-bootloop-death-blod-andorid-t3683926
To do monthly security patch updates, visit the top of the current URL. Download 3 required files: System Image .zip, boot .img file, and recovery .img file. Unzip the system image zip file. Copy the folder with all these files locally to your ADB folder.
Navigate within extracted zip file folder to find flash-all.bat file and edit. Find "fastboot -w update" line and delete -w so phone is not wiped on update. Only skip this step if you do want the phone to be wiped on update.
Boot phone into bootloader mode by pressing and holding volume down and power button from powered off state. From command prompt window, run flash-all.bat file to install update. Once done, the phone
will bootloop again.
Boot phone into bootloader mode again by pressing and holding volume down and power button. Flash updated boot .img by running command with current boot .img file name, example:
fastboot flash boot boot-fixed.img
Flash updated recovery .img, if new one was provided this month, by running command with current recovery .img file name, example:
fastboot flash recovery recovery-fixed.img
Boot phone normal using Start onscreen option.