[205guy]

My brain always stumbles on the loose-lose pair. I don't usually substitute them for each other, but I always have to think about which one to write. I believe it is because of the odd spelling and pronunciation of the pair. The extra o does not change the vowel sound, instead it changes the sound made by the s (and neither sound like "close"). Typically, the hard and soft s sound depends on the one or two s's [1]: desert and dessert.

Or it could just be the auto-correct (now in desktop apps as well, not just mobile).

[1] I hate 's for plurals, but how else would you write "esses".