Actually, #91 is an example of Connections that does one thing right and one thing wrong, IMO.
For one category, in this case there's one word among the 16 that people might, without thinking too much about it, add to the yellow category. But it doesn't belong because that one word is unlike the others in an important way.
But then the blue category is broad enough that there are at least three other words that would fit just as well as the four that are actually in it. They should give all words in any given category some distinctive trait that would disqualify other words. Make them all by Stephen Sondheim, for example, or all from the 1980s. That way, it won't be as frustrating if you guess something and the words shake their heads, it won't be as frustrating because your guess actually didn't fit.
For example, the word "train" might possibly go with either "jet, helicopter, hot-air balloon, blimp" or "tutor, instruct, coach," you'd know it should go in the second, because the first group are forms of air transportation. Then if you want to confuse people more you could add a word like "clarify" that might seem to go with "tutor, instruct," etc., but is actually a little different from those words and fits better with "brown, churn, spread."