blockchain: fix ahead of time PoW batch calc

src/cryptonote_core/blockchain.cpp

@@ -3514,7 +3514,7 @@ leave:
     // validate proof_of_work versus difficulty target
     if(!check_hash(proof_of_work, current_diffic))
     {
-      MERROR_VER("Block with id: " << id << std::endl << "does not have enough proof of work: " << proof_of_work << std::endl << "unexpected difficulty: " << current_diffic);
+      MERROR_VER("Block with id: " << id << std::endl << "does not have enough proof of work: " << proof_of_work << " at height " << blockchain_height << ", unexpected difficulty: " << current_diffic);
       bvc.m_verifivation_failed = true;
       goto leave;
     }
@@ -4328,7 +4328,7 @@ bool Blockchain::prepare_handle_incoming_blocks(const std::vector<block_complete
         unsigned nblocks = batches;
         if (i < extra)
           ++nblocks;
-        tpool.submit(&waiter, boost::bind(&Blockchain::block_longhash_worker, this, thread_height, epee::span<const block>(&blocks[i], nblocks), std::ref(maps[i])), true);
+        tpool.submit(&waiter, boost::bind(&Blockchain::block_longhash_worker, this, thread_height, epee::span<const block>(&blocks[thread_height - height], nblocks), std::ref(maps[i])), true);
         thread_height += nblocks;
       }