This happens in every app.
On my Samsung S6, whenever I place a punctuation mark inside or next to a word, it autodeletes the mark and doubles a letter in the word. For example, it changes didn't to ddidnt. When I go back and add the apostrophe, it changes to diidnt, then diddnt, then finally didnnt. This hapens to all words and punctuation. If anyone has help, please tell me.