Looks like my Adobe Reader DC was automatically updated to Version 2019.012.20040

on Wednesday, 8/22... apparently via a "Scheduled Task".   (I had turned off automatic updates in other locations).

EDIT:   It's classified as an OPTIONAL update, which "fixes specific functionality issues" (rather than being a "security" update).

The "hotfix" patch may be downloaded from https://www.adobe.com/devnet-docs/acrobatetk/tools/ReleaseNotesDC/continuous/dccontinuousaugust2019qfe.html#dccontinuousaugusttwentynineteenqfe