"On September 27, fork-observer notified me about the invalid Bitcoin mainnet block000000000000000000006840568a01091022093a176d12a1e8e5e261e4f11853 at height 809478."
"@mononaut further inspected the invalid block and found 145 transactions that were included before their parent. They, too, came to the conclusion that this likely isn’t related to Bitcoin Core’s block template algorithm. Moreover, the transactions in the block were sorted by fee before mining, which breaks Bitcoin’s consensus rules if there are parent-child relationships in the transactions."
"Marathon Digital Holdings later confirmed that they mined an invalid block and clarified that they are using a small portion of their hash rate to experiment with a new, internal mining pool software in a development environment."
"To clarify, this bug emanated from Marathon's own internal development environment. It was not related to Marathon's production pool. It was also not related to Bitcoin Core. Bitcoin functioned exactly as designed by excluding the invalid block," added the company.