Bitcoin briefly formed two competing chains after Antpool mined block 941,881 at 15:49:35 UTC and Foundry USA mined another version of the same height 12 seconds later. According to ChainCatcher, ViaBTC then extended the Antpool version with block 941,882, while Foundry USA continued extending its own branch.
Foundry USA later mined blocks 941,883 through 941,886 in succession, giving its branch the most cumulative work. Nodes then reorganized to the Foundry USA chain, orphaning the blocks mined by Antpool and ViaBTC. The affected miners lost the associated block rewards and fees, and transactions not confirmed on the winning chain returned to the mempool before being confirmed in later blocks.