Most likely, the recovery phrase is not BIP-39 compatible.
An Internet Identity-generated recovery phrase will only contain 24 BIP-39-compatible words. Some BIP-39 backup solutions only allow storing the first 4 letters, in compliance with the BIP-39 protocol. While BIP-39 was designed to only use the first 4 letters of each word, Internet Identity will not "re-inflate" the words for you, so you may need to do that to recover your Internet Identity.
Learn more about BIPs on Github.
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