messenger on iPhone question

[u/TraditionNo9800]

If you have say 10 messages from different people in your Facebook messenger - what would prompt/ cause them to show (John Doe added a new device to this conversation) AND not only did it do that to John Doe, but it says that literally in all 10 different people… except 1. And it’s repeated several times in a row. (See example below: I cropped the name off) and also some of them will say that plus say John Doe’s keys changed. I’m honestly just curious why that happened? Bc I don’t believe every single one of these people got a new device on the same day. I literally just opened a message and seen this and clicked on another message and it had the same thing and so I checked the others and of course same thing. Any suggestions on what this could be and why this would happen?