For words that have only 3 letters, there is no 4th letter. For instance with the word “increase”, there won't be any more letters afterwards and therefore should be the word "add". The word “addict” is in the BIP39 wordlist however, you might have used “addi” for “addict”. Discovering one https://socialistener.com/story4276606/examine-this-report-on-bip39-mnemonic-phrase-tool