Apparently, due to the fact that a host is considered to be active only by coincidence of pkt_id, when several copies of the program are launched in parallel, the false definition of inaccessible hosts as active occurs.
If run two copies in parallel, which should check hosts in different subnets, two ICMP-requests are sent to the network to different hosts, but sometimes the IDs in such requests coincide. This automatically leads to the identification of both hosts as active.