Error: Block recognized as orphaned and rejected #198

when syncing dev-v0.6 node from 0, it stops at block 7124 with following error:

2019-05-20 17:54:39.031 D block <344782c93726d7a75f61cda86e5030a361e981eec523f2e449b8e3b0a1d6f39d> found in main chain
2019-05-20 17:54:39.031 I Restarting adding block after idle for 1.5012 seconds
2019-05-20 17:54:39.031 D [get_estimated_batch_size] m_height: 7124  block_start: 6624  block_stop: 7123
2019-05-20 17:54:39.032 D estimated average block size for batch: 15966
2019-05-20 17:54:39.032 D calculated batch size: 359235008
2019-05-20 17:54:39.032 D increase size: 536870912
2019-05-20 17:54:39.032 D DB map size:     5535110656
2019-05-20 17:54:39.032 D Space used:      250753024
2019-05-20 17:54:39.033 D Space remaining: 5284357632
2019-05-20 17:54:39.033 D Size threshold:  359235008
2019-05-20 17:54:39.033 D Percent used: 0.0453  Percent threshold: 0.9000
2019-05-20 17:54:39.034 D tx <5005130cc301cacef7cfb8ec182e3ae91a1c00701b981f5dc3ac8ceda00e85a7>already have transaction in tx_pool
2019-05-20 17:54:39.034 D tx <d3cee11c341170bbc23a0bca7ed36ed1d61e3250c7c35ed451f5b80202ae9f3a>already have transaction in tx_pool
2019-05-20 17:54:39.034 E !!!!!!!!! difficulty overhead !!!!!!!!!
2019-05-20 17:54:39.035 E Block recognized as orphaned and rejected, id = <34d79939e67f4d3bed4cfb365af9448f495eeec36e54bdab1d717a32d5a75fb7>, height 7125, parent in alt 0, parent in main 0 (parent <b35cdac21bd62ad5df8851ac0880adc75f0a1dba1d711fbc44e06dd9b83c2a3c>, current top <344782c93726d7a75f61cda86e5030a361e981eec523f2e449b8e3b0a1d6f39d>, chain height 7124)
2019-05-20 17:54:39.035 I [x.x.x.x:34567 OUT] Block received at sync phase was marked as orphaned, dropping connection
2019-05-20 17:54:39.035 D [x.x.x.x:34567 OUT] dropping connection id 6cda56fc-50ca-4f6a-8c28-db86ea8a6725 (pruning seed 0), add_fail 1, flush_all_spans 1
2019-05-20 17:54:39.036 D Host x.x.x.x fail score=6
2019-05-20 17:54:39.036 D Pruning not enabled, nothing to do
2019-05-20 17:54:39.037 D miner::resume: 1 -> 0
2019-05-20 17:54:39.037 I [x.x.x.x:34567 OUT] [0] state: closed in state synchronizing
2019-05-20 17:54:39.037 I [x.x.x.x:34567 6cda56fc-50ca-4f6a-8c28-db86ea8a6725 OUT] CLOSE CONNECTION

when syncing `dev-v0.6` node from 0, it stops at block `7124` with following error: ``` 2019-05-20 17:54:39.031 D block <344782c93726d7a75f61cda86e5030a361e981eec523f2e449b8e3b0a1d6f39d> found in main chain 2019-05-20 17:54:39.031 I Restarting adding block after idle for 1.5012 seconds 2019-05-20 17:54:39.031 D [get_estimated_batch_size] m_height: 7124 block_start: 6624 block_stop: 7123 2019-05-20 17:54:39.032 D estimated average block size for batch: 15966 2019-05-20 17:54:39.032 D calculated batch size: 359235008 2019-05-20 17:54:39.032 D increase size: 536870912 2019-05-20 17:54:39.032 D DB map size: 5535110656 2019-05-20 17:54:39.032 D Space used: 250753024 2019-05-20 17:54:39.033 D Space remaining: 5284357632 2019-05-20 17:54:39.033 D Size threshold: 359235008 2019-05-20 17:54:39.033 D Percent used: 0.0453 Percent threshold: 0.9000 2019-05-20 17:54:39.034 D tx <5005130cc301cacef7cfb8ec182e3ae91a1c00701b981f5dc3ac8ceda00e85a7>already have transaction in tx_pool 2019-05-20 17:54:39.034 D tx <d3cee11c341170bbc23a0bca7ed36ed1d61e3250c7c35ed451f5b80202ae9f3a>already have transaction in tx_pool 2019-05-20 17:54:39.034 E !!!!!!!!! difficulty overhead !!!!!!!!! 2019-05-20 17:54:39.035 E Block recognized as orphaned and rejected, id = <34d79939e67f4d3bed4cfb365af9448f495eeec36e54bdab1d717a32d5a75fb7>, height 7125, parent in alt 0, parent in main 0 (parent <b35cdac21bd62ad5df8851ac0880adc75f0a1dba1d711fbc44e06dd9b83c2a3c>, current top <344782c93726d7a75f61cda86e5030a361e981eec523f2e449b8e3b0a1d6f39d>, chain height 7124) 2019-05-20 17:54:39.035 I [x.x.x.x:34567 OUT] Block received at sync phase was marked as orphaned, dropping connection 2019-05-20 17:54:39.035 D [x.x.x.x:34567 OUT] dropping connection id 6cda56fc-50ca-4f6a-8c28-db86ea8a6725 (pruning seed 0), add_fail 1, flush_all_spans 1 2019-05-20 17:54:39.036 D Host x.x.x.x fail score=6 2019-05-20 17:54:39.036 D Pruning not enabled, nothing to do 2019-05-20 17:54:39.037 D miner::resume: 1 -> 0 2019-05-20 17:54:39.037 I [x.x.x.x:34567 OUT] [0] state: closed in state synchronizing 2019-05-20 17:54:39.037 I [x.x.x.x:34567 6cda56fc-50ca-4f6a-8c28-db86ea8a6725 OUT] CLOSE CONNECTION ```