iOS autocomplete for the longest time was just absolutely insane. It would inject the selected suggested option into the middle of a word when I was correcting a spelling error. Really made me feel like I was doing something weird but I swear I was being normal for once.
As well as what you describe, it starts to hate me uncertain words. I have a colleague called An. iOS hates this and changes it. It does it when you are a line away from the word too. It’s painful.
I have to type ‘TE’ regularly too, an abbreviation for echo time.
If you’re on iOS, try it. I have resorted to typing TEE and then hitting delete to remove a E and then carrying on.