As the security requirements increases, 5G slicing-enabled Internet of things needs to adopt end-to-end standalone networking, which limits the consensus convergence of mobile blockchain. Although the rise of FIBRE (Fast Internet Bitcoin Relay Engine) gives a huge promotion to block propagation, existing approaches cannot consider the influence of link outages among 5G slices on mobile blockchain. In this paper, we focus on decreasing the block propagation time among blockchain peers under the scenario where link outages among 5G slices exist. A predictive fast consensus convergence (PFCC) scheme is proposed for mobile blockchain over 5G slicing-enabled internet of things. In PFCC, federated semi-supervised learning is used to learn the features of withdraw packets, reroutes the packets of blockchain peers, and ultimately reduces the scale of link outages quickly. With PFCC, different blockchain peers located in standalone 5G slices of IoT can transact local sensing data more efficiently. To the best of our knowledge, this is the first work to improve the consensus convergence speed of mobile blockchain by optimizing communications between 5G slices. Experiments shows the feasibility of proposed scheme.