(separated from my other answer because this one has more opinion than explanation)
If you agree that the "XY Problem" is only another (more specialized) term for "Use of wrong working hypothesis", as illustrated and explained here, and similar to the "Einstellung effect" explained here by @Jonathan Benn…
We can think in terms of some main situations:
Rush situation: the wrong hypothesis is only a language or over-simplification side-effect, that can be corrected by the user with a little more attention, and investing more time editing the question.
Normal situation: as in the illustrated Missing Square puzzle, you do not know that your hypothesis is wrong. This is the main situation to discuss here (!).
So let's put focus on the normal situation.
SOLUTIONS/ATTENUATORS
The "XY problem" is a valid problem!
The Stack Exchange question is to show a problem. If my question helps to show that the real problem is my wrong hypothesis, it is OK! It is a first step, and perhaps I will not need any other questions after obtaining the correct hypothesis (and trying to solve by myself).
Example. See my rushed question about "self axis that fails";"https://stackoverflow.com/q/28863328/287948"; the real problem is that @attribute::self does not exist, so it was a wrong hypothesis on the title of the question.
The help/mcve solution has limitations
Stack Overflow's help/mcve rationale: "How to create a Minimal, Complete, and Verifiable Example", can be used to avoid the XY problem.
But the cost of edit (time and attention expensive), and the perception that it is a kind of pollution in your text (a "bad marketing" for the question), are downsides.
It's correct also to simplify the problem and explain with more focus on the point.
Best practice
Train users of Stack Overflow to check if the simplification makes sense. Algorithm for a good question:
Try to create an MCVE.
If an MCVE is not practical, try at least to simplify.
2.1. Test, check for inconsistencies, simulate the reader… and review. Does your simplification produce something strange, change the context? Review to avoid errors.
Listen to the comments about your question, and try to clarify, try to work editing the question if necessary: if there are people commenting, it is a notice that you can invest more time in your question.
The wrong hypothesis is not self-evident, but when we simplify, we amplify the wrong effects, and it becomes more evident.
PS: On the other hand, when we explain and show all the details, all the context, and check the real point, the assembly of the problem (like when using mcve), the inconsistencies also show with more evidence.
