Isolated breakdown (IBD) process is a lightning phenomenon that was rarely reported in the past. It is characterized by radiowave pulses typical for preliminary breakdown before negative cloud-to-ground flashes, which fail to evolve into return strokes. We identified 128 IBD pulse trains in measurements collected in the Mediterranean by a broadband receiver (0.005 – 37 MHz) in 2015 and 2018. By combining these records with concurrent Lightning Mapping Array measurements of very high frequency radiation (60 – 66 MHz) emitted by in-cloud discharges we investigate the development of each discharge. We identify two scenarios: either the discharges continue to propagate almost horizontally for more than 150 ms (73%), or they disappear sooner, typically within several tens of milliseconds (27%). Using numerical modeling, we verify that a potential barrier inside the thundercloud caused by a strong lower positive charge center could indeed block further propagation of lightning leaders toward the ground.