When a squad disbands, you're supposed to no longer have people in the "squad chat", however for the last.... Very long time? At least half a year, that doesn't happen. Squad disbands, and some people are left behind, and after playing with multiple squads I end up having a mix of 2-3 squads in the same chat (till either I log out, or they do).
I don't know what exactly triggers it, but I notice it a lot with the Zariman missions and Deimos.