Colud you please check the pr_sys_statusnodes table and see the entries for pyindexeraddress and pyindexerstate column. If the ip address for the master node is incorrect and state is failed. Please truncate the table and restart the system. However please go through below 2 troubleshooting videos for information on the indexing issues:
Just go to search landing page and check the work index status which should not have a negative value, try to rebuild the work index. verify pr_sys_status_nodes table so that all rows with different node ids have status as active, if not truncate the table and try to rebuild the index.