When a device discovery is started, the already known devices are immediately returned using deviceDiscovered signals. This happens in the start function before the discoverytimer is started. When stop() is called in the deviceDiscovered slot, the adapterBluez5 is deleted and the discoveryTimer is stopped (which might not even be started). After the known devices are reported in the start function, the discoveryTimer is started. This times out 20 seconds later. In the timeout slot, adapterBluez5 is used which is 0 causing a segmentation fault.