What of the following caused (probable) fusels?

[Pappa_Bjorn]

I've gotten the same off flavour/scent in two brews; one mead, one gose. It's highly reminiscent of paint solvent/mineral spirits, and describable somewhat like combusted diesel, machine grease, non-ferric/ferrous minerals/metals (or dust of these), being mildly peppery, flat and greasy in taste yet with no texture, being not sour/tangy, and being associated by me with metros, mechanic workshops, old machinery in museums, etc. Thus I suspect it's fusel alcohol(s), though I haven't gotten the privilege of smelling foul moonshine for a proper comparison yet.

Both brews share...​

1. ...US-05 yeast,
2. ...initial ferment temp @18°C/65°F,
3. ...ferment temp raised to 23.5°C/74°F @t+10d,
4. ...low pH must/wort (caused by grapefruit juice in must, and acid malt mash in wort),
5. ...added citrus zest (which smelled very fusel-y in the hop bag w. lemon zest from the mead carboy),
6. ...longer bottle conditioning @ high temp. sliiightly reducing off-taste presence.

I've used US-05 in two other ales in the same location at the same temp., yet these came out great.

What differs in these two vs. the failed ones is that...​

1. ...the ales fermented only @23.5°C/74°F - no cold-to-hot transfer,
2. ...due to higher temp. the ales fermented faster and more violently,
   
3. ...the ales did not have a lower-than-avg. pH wort/must,
4. ...the ales did not have citrus zest (with citrus oils still inside),
5. ...the ales had a lot more hops.

A) Am I right in my fusel diagnose?
B) If so, what of the above likely caused the fusels in the gose/mead, but not in the two ales?
(Made a similar thread for gose only before both brews were finished but I'm re-making for clarity/reduced clutter/added info. Apologies if considered spam)

 

[microbusbrewery]

It's kind of hard to say for sure based on description alone. Usually it literally comes across as a hot character at lower concentrations. If it gets really high, it can literally smell like someone opened a container of paint thinner or nail polish remover. At the ferm temps you cited and with the low gravity typically associated with a Gose, I'd be pretty skeptical about it being a fusel issue. Yeast can generate a lot of nasty stuff at elevated temps, but that shouldn't come into play until you start getting into the upper 70s and higher. Did you add any new equipment for these batches? New gaskets, new tubing, anything along those lines? Excessive oxygen exposure?