It's an invalid deposit.
The deposit contract cannot verify the deposit signatures yet. This might change with the Berlin hardfork though if we can get a BLS precompile. But that's not set in stone yet.
Currently, the EVM is unable to process the BLS signature of the deposit data. This has the (im)practical consequences that Ethereum 2.0 clients (and other tooling such as your script) not only need to catch the deposit events, but also verify the BLS signatures manually in the post-processing.
Reasons for invalid signatures can be outdated or misconfigured tooling/clients to generate the deposits. In most cases, wrong fork versions are used.
Edit 0: EIP-2357: Precompile for BLS12-381 curve operations
Edit 1: Also check the deposit contract
emit DepositEvent() happening only after some sanity checks. It even fires if the deposit would fail on the data root and merkle tree checks further down.