As one of the tweet commenters noted, this could be due to lack of interest from Republican moderates who are concentrated in Dem strongholds...
It's not just moderates, Republican enthusiasm is just about non-existent in Franklin County atm.
If moderate Republicans are the reason, shouldn't Hamilton see a bigger drop-off than 3%? At the same time, I can't deduce at this point whether this is the first bad sign for Hillary in OH. Absentee is dominated by Republicans in most states.
I'm not just talking about moderates, it's Republicans in general (also the Cincinnati suburbs are home to some pretty right-wing Republicans, very different from what you'd find in Franklin County). Also, I was just talking about Franklin County.