Again, Is The Trolley Problem a Fallacy?

No. It's a moral dilemma that pits deontological against consequential reasoning. If fallacies exist it is only in the explanations one puts forth to justify their decision of whom to save or sacrifice.

"Is the Trolley Problem a (logical) fallacy?" -- No, it's not.  That's because it isn't an argument, it's a question to be answered.

In my experience, this problem has been used in the context of ethics, rather than logic.  Not only do I see the problem as an ethical one (and not a logical one), I don't see an argument here at all.  In its purest form, the Trolley Problem doesn't present a preferred outcome; rather, it poses a problematic dichotomy and asks for the "best" (or perhaps least bad) option.  Those responding to the question posed might present arguments and those arguments might or might not include fallacies; however, the question isn't a fallacy.

As I understand the Trolley Problem, it is structured as a situation in which there are exactly two options (i.e., an actual dichotomy) in which one is asked to balance the moderate potential for harm to a large number of people against highly likely harm to just one individual. Ultimately, the question asked is, " Is it better to accept a high level of risk to an individual or to accept a lower level of risk for a group? " 

The only way I can see it it being a logical issue (so that we could debate whether it's "good" logic or "poor" logic, i.e., a fallacy) would be if we placed it in the context of a particular belief structure.  If, for example, we were part of a group for which a basic tenet of our belief structure is that our duty is to do the most good (or the least harm) for the greatest number of people, then the argument would go along the lines of:

A ) When faced with a choice, we must always choose doing the most good (or the least harm) for the largest number -- presumably accepted by "our group" as an axiom and therefore assumed to be true.

B ) Switching tracks will somewhat reduce the risk for the larger group, although it will significantly increase the risk for a single person -- a part of the problem's typical situation that we are asked by the problem to accept as true.

C ) Therefore, switching tracks is the correct choice since it follows our group's basic tenet of fostering the greatest good for the largest number.

Such an argument doesn't seem to have a fallacy.

On the other hand, let's assume the argument went like this (for members of the same group):

A ) When faced with a choice, we must always choose doing the most good (or the least harm) for the largest number -- presumably accepted by "our group" as an axiom and therefore assumed to be true.

D ) Switching tracks will almost certainly create huge harm and perhaps even death to for the individual on the other track -- a part of the problem's typical situation that we are asked to assume to be true.

E ) Therefore, switching tracks is the wrong choice since it would potentially kill an individual.

Without getting into the ethical debates associated with the Trolley Problem (and others like it) this conclusion may or may not be a correct statement, but it doesn't follow from the premises presented ... therefore, this argument presents a fallacy.

What I've tried to present are two arguments , one without a fallacy and one with a fallacy.  If I've done it correctly, we have an example of a fallacious  argument  and one with a valid argument -- since arguments can include fallacies.

However, back to the original question ... "Is the Trolley Problem a (logical) fallacy?"  No, it's a problem .  The problem can lead to various arguments, some of which might include a logical fallacy ... but the problem itself isn't a fallacy.

To put the Trolley Problem into a more current context, let's consider vaccinations in the midst of a short supply of vaccine: " Is it better to provide two doses to a smaller number of individuals or a single dose to a larger number of individuals? "  Neither is a great option but it's not so much a question of logic as ethics -- unless we're part of a group with a basic tenet like "helping a large number (even a little bit) is better than helping just a few" or "protecting a small number to the fullest degree possible is better than protecting more to a lesser degree".  From either of these positions, one can construct valid, logical arguments (and fallacious ones).  

However, the choice of which position one accepts as "right" is an ethical, and not logical, decision.