Bitcoin mining company Marathon Digital (MARA) has mined an invalid Bitcoin block at height 809478, according to several developers, miners and researchers.

Anonymous Bitcoin developer “0xB10C” wrote on X that MaraPool had a “transaction ordering issue,” this was confirmed by CasaHODL co-founder Jameson Lopp.

The invalid Bitcoin block was rejected by other node operators. The block contained a transaction that was ordered incorrectly with a spending output transaction, thus the block was invalidated, according to BitMEX Research.

Marathon Digital did not immediately respond to CoinDesk’s request for comment.