osm2po - Repair topology before pgrouting / No results of pgrouting

My goal is to calculate lots of distances along the streets. I followed http://workshop.pgrouting.org/ tutorial except that I used osm2po instead of osm2pgrouting to import osm file. The only problem I'm facing now are gaps in results - Dijkstra algorithm seems to fail in finding the route between two nodes of the network in 10% of cases. It simply returns nothing, empty table. I suppose the problem is with the map, that it's not "routable enough" (I can't imagine any other reason). Did anyone have the same situation? Do you know how to fix it?