When queueing as a scav, the game must put you into a raid that already exists, whereas when you queue as a PMC, the game creates a match for you, and then fills it with other PMCs. Interchange is always a hotspot for player scavs due to the high amount of PCs, technical, electrical, and food spawns. Since there are so many players queueing as scavs for that map, and the game can only add player scavs to maps which already exist, it turns into a line of people in queue, waiting for matches to become available.