Bip39 Invalid Mnemonic. The only real rationale All those letters are listed is to make it much easier for our human brains to read through them and possibly memorize our recovery phrase. These words are pulled from a particular list of 2048 words. They can be found here or listed https://enrollbookmarks.com/story18715396/what-is-a-seed-in-r-the-2-minute-rule-for-seed-phrase-generator-checker-seedgen