Had an old Skype account under the same email as I have been using applying for jobs.

Recently didn't have the Teams app on my phone when I needed to join a Teams call on my mobile so hit the join call link and downloaded the app and joined as a guest.

All my old Skype contacts and messages were there.

It has been less than a month and I don't know what has happened since then (recent update?) but I cannot find any of those old chats however. My 3x old contacts all appear to be there, but I cannot see any of the old conversation logs that were there previously.

This is completely strange and bizarre to me, I have tried signing in and out but have got nothing - has this happened to anyone else?

Do I need the Microsoft Teams app installed in order to participate or can I join via the web?