Google resolved the Package File Invalid issue, so it's clear that it was indeed independent of the Play Store version.
Having torn down the APK, the changes are:
Updated plural translations for the following locales: bg, es-rUS, fr, id, in, ja, ko, ms, pt, pt-rPT, ro, ru, sk, sl, th, tl, tr, vi, zh-rcn
Minor changes to the Search Adapter and Play Tab Container. I can't tell what these changes are exactly, but they have something to do with item counts, query suggestions, and layout width. Probably bug fixes.