I haven't found that to be the case. The only oddity I've found recently is that Marauders seem to come in pairs. This might be because as soon as I discover the first one, I kill it immediately, so when I search again (immediately after that) I get another Marauder. This tells me that the discovery of Marauders might be timed. There might be an- as yet- undiscovered time cycle where marauders are discoverable. For example, it might be that a Marauder can be discovered, but only during a 5 minute window that occurs every 15 hours. Or something like that.