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One of my sites is in an identical situation. The home page is showing an old cache date, whereas all internal pages are showing a recent cache date. This all happened when this "update/rollback/tweak" began last week.
I know for a fact that G HAS indexed/cached the home page with a more recent date than the one it currently shows in the SERPS, so G DOES know about it.
Once this situation (whatever it is) is complete, I would expect G to be showing a more recent cached date for the home page too.