Bitcoin has been criticized for its stability. In this paper, I discuss about two topics among the criticism, its weak block synchronization and vulnerabilities that enables partitioning attacks. First, weak block synchronization is claimed by recent several studies, arguing that blocks in the Bitcoin is slowly propagated. The studies reference data from two types of Bitcoin monitors, Bitnodes and customized supernodes. I test if the two monitors are working correctly, find and fix flaws, and confirmed that the block propagation is fast enough. Next, several vulnerabilities are claimed in the Bitcoin for past several years, arguing that the Bitcoin network could be partitioned either with low cost, stealthy manner, or large scale. Here, I discuss about how long would the attacks last, which is not discussed at original studies. I found that two original attacks would not last longer than 10 minutes, which is usually harmless for the Bitcoin network. I further optimize the two attacks, and concluded that optimized Erebus attack can successfully lasts for an hour, but the optimized SyncAttack still cannot last long enough time for practical attack.