Something happened to my brain lately and I started to make this kinds of typos in English, which I didn't before.
I'm 32, but I noticed I started making similar mistakes around 28 or so. Occasionally I write out words which are completely wrong, but sound similar.
It's as if one part of the brain is doing the thinking, and another one is "listening" to it and transcribing/typing it out, making mistakes.
For a little while I was a bit worried, but I then realized nothing else had changed, so I've just gotten used to it and like to jokingly say "I've become so fast at thinking that even I can't keep up!"
I suspect that as I got more vocabulary (and more languages) and started to actually speak the language more, I remember the "sound" of the word where I used to remember the spelling before. Like "it's" and "its" wasn't a problem before, but now I catch it somewhere in the text. At least I consistently write more than 50% of the articles nowdays. Languages are weird.
While I was writing the reply, I considered giving the absolutely exact same explanation, which I agree with, down to the example you gave.
Two examples in portuguese that always trip me up, and absolutely never used to before are (i) "voz" (voice) and "vós" (you); and (ii) "trás" (back) and "traz" (bring).
I also do a lot more code-switching.
I'd say they found it, but I love the conspiracy theory :D :D :D