These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Scrappy Mechanic: Wolfram Alpha's mathematics engine is essentially a limited version of Mathematica, so it would make sense if it wouldn't be able to understand equations beyond a certain complexity. However, it seems instead that whethero or not Alpha accepts a given query is entirely random. You can put in a complicated query and Alpha will understand it just fine, but make one tiny, minor edit (e.g. change "2x" to "3x") and all of a sudden the program refuses to comprehend it.