If you do X correctly you will never make a mistake.

There are two categories here: one of true statements, and one of unfalsifiable/false statements. Consider a true statement:

If you chew your food properly, you won't choke and die.

While I guess it might be possible for one to choke and die from properly chewed food, the statement is for the most part true, so no fallacies. Notice while not 100% accurate, it is close enough for use in casual conversation (without being pedantic).

Now for a unfalsifiable/false statement:

If you pray correctly, you will always get what is best for you.

This would fall under unfalsifiability , but it can also be simply not true.

As for your examples, I would think they are more untrue than anything else. There is subject-specific information needed here, like the proper operation of a wood chipper as well as understanding how the machine functions (and malfunctions). I am guessing that even with perfect form, the machine does not cooperate all the time. If this is the case, your boss is just wrong. He would be more accurate saying something like, "If you feed in the branches correctly (and he clearly explains the correct way), then you are far less likely to run into clogging." Unlike the choking example, I am assuming here that malfunctions due to "correct" operation are common, but I can be wrong.

Hi, Jacob!

My two cents is that the fallacy you are looking for may be the post hoc ergo propter hoc. Your boss thinks that because the machine was clogged after you fed branches in a certain way, the machine was clogged because of how you fed the branches in. 

By the way, the operator’s manual defines the correct procedure for feeding in branches. Perhaps ask for it and check your work against it. 

Anyways, you believe your technique is correct and that your boss is blaming you for a clog that was not your fault. You may point out to your boss that machines can fail—such as by becoming clogged—either because of user error or because, and this is what your boss has rejected without apparent reason, the machine‘s own imperfections manifested. Both machines and people are imperfect and either one’s imperfection may cause a malfunction. It’s not always the operator’s fault. If you think the problem is in the machine and not in you, show that you are doing everything right by comparing your technique to the steps in the operator’s manual. In the meantime, reasoning as your boss does that the problem is with your way of feeding in branches because the clog happened after you fed in branches is “after this, therefore because of this” fallacious reasoning. 

Thank you, Jacob

From, Kaiden 

We would have to accept this proposition: if you feed in branches correctly, then the chipper doesn't get clogged. 

When you say that "...sometimes the chipper gets clogged when I feed in branches correctly..." you disagree with what your boss said; you fed in the branches correctly but it got clogged. 

The statement "...sometimes it does not get clogged when I feed in branches incorrectly..." is a little bit more involved. Consider this analogy:

Person 1: If you buy tickets early, you'll be able to get front seats.
Person 2: That's not true because I had gotten seats late before to that event and still got front seats.

In symbols: 

~P & Q <=> ~(P => Q) <=>~(~P OR Q) <=> P & ~Q. But P & ~Q <=> ~P & Q is false (set P to true and Q to Q to false).

The first biconditional is false. Set P to be true and Q to be false. This could be a questionable cause depending on your evidence (how many trials of incorrect feedings do not clog the chipper). 

Your examples make me think of the distinction between “necessary” and “sufficient” conditions. For example, flour is necessary for making good bread but it is not sufficient – other things are needed, in addition.

for the wood chipper, it seems that feeding the braches would be necessary but I suspect that’s not all it takes.  I suspect the chipper must be properly adjusted, running at the correct speed, etc. and that the branches need to be of the correct size, shape, etc.

The examples also make me think of the distinction between “if” (the normal meaning of the word) and “iff” (“if and only if”).  You’ll get rich if you save money … but … you’ll get rich “iff” you make lots of money, you save a bunch of it, you don’t invest badly, etc.

i don’t see fallacies as much as I see potentially false premises.