I don't know if this is a known behavior. I dropped out at this threat 4 NHSS and there were 2 Scouts and a Thargoid Sensor. I killed them and while I was picking up the mats 2 more Scouts had jumped in and they had kept spawning in pairs, regardless I killed them or not. At first I thought they were spawning around me and I just farmed them, synth'ed, repaired and kept going until I lost them. Then I realized they were spawning around the Sensor, not me. I don't know if picking up the Sensor would make them spawn around me or it's a fixed point in the instance. As expected I couldn't relocate the Sensor, I was in deep space, no way to tell direction. My COVAS kept saying "frameshift anomaly detected", however I couldn't locate where they are and nor could they located me. I tried to see little dots flying around or parallax effect of the "portal" they use in the distance but no luck.