Did you properly prime the head before using?
If not, most likely the wicking material got scorched / burned.
Hot & harsh could be from scorched wicking material reducing wicking ability or PG % or nic mg.
Seems most folks use 3 - 6 mg nic, & higher % VG than PG.
To prime a head, Drip drops onto the wicking material from the top until it is fully saturated, then install in base, fill tank thread together, take a few un powered primer puffs, may need to hold a finger over the airflow holes.
You should see bubbles rising from the wicking holes occasionally if it is wicking correctly.