Leader-based Byzantine Fault-Tolerant (BFT) protocols heavily rely on an honest leader to guide other nodes to reach a consensus. To elect the current leader, the HotStuff BFT protocol proposed to use a pacemaker, which also ensures the liveness of the BFT protocol. In this paper, we carefully inspected HotStuff BFT and discovered that their pacemaker implementation contains a serious vulnerability that prevents the honest nodes to synchronize to the same leader. This allows us to construct two liveness attacks, Freezer attack and Constant-time Freezer attack, that stop HotStuff BFT from reaching any consensus. Notably, the Constant-time Freezer attack can be carried out in constant time, disregarding the number of honest nodes, and one single Byzantine node can launch this attack. In correspond to this security vulnerability, we design a secure and efficient view doubling synchronizer that provides protections to HotStuff's pacemaker and has comparable efficiency as other existing view synchronizers.