As the temperature increases, the average speed and energy of the particles increases. Then the rate of ionization through collisions increases. The increasing ionization rate for temperatures in excess of about 10,000 K means the number of H atoms decreases. The decreasing atom density leads to a weakening of the hydrogen absorption lines. The answer is contained with Q1 above.
Molecules are the signature of cool gas.
Molecules and ionized helium cannot coexist in the atmosphere of a normal star. The simplest explanation for the observation is to suppose that the single star is in fact a double star. One star is hot. The other is cool. Both have similar luminosities so that they contribute about equally to the spectrum.