She went online and discovered that her name had also been flagged as an inactive voter. The state was in the process of removing her from its voter rolls.

“I voted three times last year,” said Ms. Miller. “I don’t think we have any idea how many other individuals this has happened to.”

Ohio, where the Democratic presidential candidates are set to debate Tuesday, is both a battleground state and the site of some of the country’s strictest voting laws, from voter ID requirements to a “use-it-or-lose-it” provision that lets officials drop voters seen as inactive.

The combination has led voting rights advocates to contend that parts of the state are regularly disenfranchised, largely in purges aimed at those who have died or moved away, but which also hit real voters who don’t learn they can’t vote until Election Day. Election officials in other battlegrounds such as Florida, North Carolina, Georgia and Texas regularly purge their voter lists as well.

This year, a group of elected officials in the state, mostly all moderate Republicans, tried to answer the concerns with an experiment of their own: Rather than purge the voter rolls behind closed doors as had been done in the past, the government released the full list of those to be removed this summer, and gave the list to advocacy groups. The groups said they found the list was riddled with errors.