Apologies for the long reply in advance. Due to a shortage of time (don't we all wish for more of it?), I'll summarize and address the first article you linked to.

Paragraph 1: Alt-right figure A identifies as libertarian. Alt-right figure B identifies as a former libertarian.

Paragraph 2: Alt-right figures C and D identify as libertarian. Alt-right figure E kicked out of libertarian conference. This last example seems to contradict the article's thesis.

Paragraph 3: There are many more conservatives than libertarians, thus a disproportionate number of today’s prominent alt-righters began as libertarians. Plain non-sequitur.

But suppose the conclusion were true. The fact that many X began as Y does not mean many Y will end up as X. Thus we have another fallacy. P(future alt-right | past libertarian) ≠ P(past libertarian | future alt-right).

Paragraph 5: Both libertarians and paleoconservatives are anti-interventionist. Ok? A shared belief does not make a shared ideology.

"And yet, it seems observably true that libertarianism is disproportionately a gateway drug to the alt-right. Again, the question is… why?"

The article has provided zero evidence for this claim, yet simply asserts it as "observably true". This is begging the question.

Paragraphs 8 and 9: Finally we get something interesting. A historical link between a subset (paleolibertarianism) of A (libertarianism) and B (the alt-right movement). None of this, however, supports the article's premise that there is an "insidious pipeline" from A to B, or that the former is "disproportionately a gateway drug" for the latter. This is a bait-and-switch.

Paragraph 10: Libertarianism is an unpopular/provocative view. Some people are drawn to unpopular/provocative views. Some of those people end up "merely passing through a libertarian phase" on their way to alt-right views. Therefore...?

Paragraph 11: Libertarianism takes a principled stance on freedom of speech, not just when it suits them (unlike the alt-right). Ok.

Paragraph 12: "Ultimately libertarianism is about peaceful cooperation―markets, civil society, global trade, peace." So libertarianism and fascism/alt-right are antithetical, which undermines the consistency of the phrase "libertarian fascism".

Paragraphs 13-15: Alt-right figure F describes his conversion from libertarianism to alt-right ideas.

Paragraph 16 points out the obvious: Cantwell was simply using libertarianism “as a shield for expressing a lot of disturbing viewpoints.”

The last few paragraphs boil down to the idea that some alt-rightists passed through a self-described "libertarian" phase. True. But this has nothing to do with the idea that there is an "insidious pipeline" from libertariansm to fascism, or that the former is "disproportionately a gateway drug" for the latter.

I agree with the conclusion that libertarians should distance themselves from alt-right and fascist ideas. After all, they're antithetical to libertarianism.

Let's take a step back from the article and return to the original comment. The GP used the phrase "libertarian fascism", yet nothing in the linked article supports the existence of such a thing. The article describes how alt-rightists abandoned libertarian ideas. It also describes a few public figures who claim they're both libertarian and alt-right, while being repudiated by other libertarians for the inconsistency of such a position. This is far from showing that libertarianism and fascism are ideologically compatible, as the phrase "libertarian fascism" seems to imply.

"Libertarian fascism" is a literal contradiction.