If you added sorbate I'm not sure it will restart. Exposure to
temperature over 30-35 C can cause the yeast to die off too early.
That could be what happened.

A better check of residual sugar (RS) is the Clinitest tablet by
Bayer. You add 10 drops of wine to a test tube and one tablet; then
compare to a color chart provided by Bayer. Using the 2 drop slabs of
color you divide by 5 to get RS. You want a dry wine to be less than
0.25% RS.