Lots of thoughtful ideas (and some I hadn't considered before).
I am another vote for
@Atomic toys issue being hardware vs. liquid related. I am almost entirely a tank (vs. dripper) user and I have experienced this pretty uniformly across the board with the 8+ tanks I have used (including both mfg. coil heads and rebuildables).
Two things I have found that will make this "harshness" go away almost immediately is to either: do a couple (2-3) of short "priming" puffs BEFORE taking my normal puff (I'm a direct-to-lunger); or press and hold the fire button for a second or two (waiting to hear the sizzle) BEFORE taking my normal puff.
I don't know if this is more of a wicking related issue, or temperature related, or a combination of both. I just know that it does make the problem go away right away (for me anyway

).
As a side note: this also seems to coincide with the times when my tank is most likely to drool/leak from the air intake slots. This is more of a dribbling effect vs. a flood like you might expect from an overfilled tank or improperly sealed tank. It also seems to have a direct relation to happening after periods of heavy vaping vs. intermittent vaping. I am guessing that it might be a result of condensation collecting, and as the tank is allowed to cool, the condensation settles to the deck, and if sufficient volume is reached; dribbles out the air channels. (Writing this just made me think that a partially obstructed airflow could also be a contributor to the harshness as well.) Removing the tank, loosely wrapping the tank bottom in a tissue, and gently blowing through the drip tip, gets rid of this problem.
This is all purely speculation on my part so please take it only as such.
Are you also getting an unussual nicotine rush/buzz with these extra-harsh hits? Or just the harshness itself? I would think if it was a settling/separation issue you would also be getting the rush of an excessively strong e-liquid along with the harshness/throat hit. If it is only throat hit I would stay with my initial thought of hardware vs. liquid separation.