For words that only have three letters, there is absolutely no 4th letter. For instance with the word “insert”, there aren't any much more letters Later on and so need to be the word "add". The word “addict” is while in the BIP39 wordlist but you might have applied “addi” https://bookmarkindexing.com/story19037903/new-step-by-step-map-for-ledger-seed-phrase-bip39