Bitcoin mining vardiff controllers can waste energy during power cuts

Bitcoin mining vardiff controllers may continue to demand work based on previous speeds even after a hashrate reduction, leading to ongoing electricity consumption while accepted shares become scarce. Bitcoin Optech highlighted this issue on Sept. 18, referencing an analysis by mining engineer Eric Price from July. The analysis focuses on pool-assigned share difficulty rather than Bitcoin's network difficulty, indicating a controller weakness rather than widespread miner losses. When pools assign share difficulties, they are typically easier than Bitcoin's block difficulty. If a miner slows down sharply, the controller may not adjust the difficulty correctly, resulting in fewer shares being submitted. This issue can persist if no new shares trigger a recalibration. Historical events, such as a January 2026 U.S. winter storm, demonstrated a significant drop in network hashrate as miners reduced power use, but this was not linked to vardiff issues. High share difficulty does not eliminate a miner's expected credit over time, as pools can assign more weight to rare high-difficulty proofs. The Stratum V2 reference implementation mitigates permanent freezes by recalculating difficulty on a timer. However, the effectiveness of this recovery method can vary based on channel age and share arrival patterns. Operators can now test these behaviors using tools like MARA Foundation's shape-proxy, which allows for local share acknowledgment while controlling upstream shares.