Just join a normal multiplayer lobby and see it for yourself. You'll be on some other squad randomly and people will continue to leave and join randomly to your squad too. Not willingly.
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**UPDATE:**
Looks like the group hop **only happens when you spawn** (after you die), if you don't die you don't hop groups.
It happens on the **precise moment you spawn in with your character** and it seems like there is a **50% chance** of it happening as you can see on the video below of me testing:
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[[ https://www.youtube.com/watch?v=JT_MWCM-sus | youtube link ]]
I suppose that there is some code that manifests itself on the process of spawning, and it causes this bug. It should be a quick fix.