If Mr. Scott ultimately prevails by a margin of 10,000 votes or less, the undervotes in Broward County could be what cost Mr. Nelson the race.

Broward County has reported about 25,000 fewer votes cast for Senate than for governor, a difference of about 3.7 percent. That means voters left their Senate choice blank, or the choice was not counted because of a tabulation error like an equipment problem. This is highly unusual, and there’s nothing like this discrepancy elsewhere in the state. Immediately across the county line in Miami-Dade County, about the same number of people voted in the Senate race and the governor’s race.

There are two distinct patterns of undervoting in Broward County.

Undervotes in the 24th Congressional District

A particularly large number of undervotes came in the part of Broward County that belongs to the 24th Congressional District, a discrepancy first identified by Matthew Isbell, a Democratic consultant. There, the undervote is about 9 percent. In other parts of that congressional district — in Miami-Dade County — there’s no significant undervote.

One possibility is that there’s some kind of tabulation error, because the scale of the undervote is so significant. If that’s true, the votes could be recovered in a recount.

If the undervoted ballots were similar to those of other voters in each precinct and were recovered, they would add a net 1,500 votes to Mr. Nelson’s total.