https://github.com/code-423n4/2023-10-party/blob/b23c65d62a20921c709582b0b76b387f2bb9ebb5/contracts/signature-validators/OffChainSignatureValidator.sol#L58
When OffChainSignatureValidator checks a given signature, it uses ecrecover to calculate the address that signed the input message:
When provided an invalid signature, that is possible because v is not validated, ecrecover may return address(0). 
While this does not represent an immediate threat, because address(0) cannot hold NFTs in the current Party implementation (so a separate check in isValidSignature would fail), in the future this missing check could be part of an attack path.
Consider implementing in-depth defense by:
