The linked transactions have a large number of sigops (241). Default bitcoin core transaction selection treats sigop's as though they have a larger size than they do. This means that these transactions are treated as though they have a significantly lower fee rate (half in this case) https://github.com/bitcoin/bitcoin/blob/82ba0f80a0b56bb160c8be1fddd82dbbc4fb3947/src/policy/policy.h#L37 static constexpr unsigned int DEFAULT_BYTES_PER_SIGOP{20};