We do not store previous conversations on the device or browser. Switching between two Messenger Tokens will remove the session token from the device, which also removes the previous conversations.
We only show previous conversations as long as the session token is active. If the Messenger client loses the session or it expires, the previous conversations are lost. A session token remains active for 7 days. The 7-day counter will be reset to zero if the client uses an existing session token against the backend (e.g., through the IdentifyMe event), thereby extending the session for another 7 days.