Have you noticed that your chat History / conversations missing every time you sign-out / sign-in on Lifesize Cloud Client?
I suppose you have not allowed XMPP (TCP port 5222) on your network.
Lifesize Cloud (CHAT) Services primarily uses XMPP servers for Chat Collaboration. We also use SIP Chat as a back up service. In case, where you have not allowed TCP port 5222, you still would be able to chat with your peers in the Lifesize Cloud group and other Lifesize Cloud groups. But your conversations will be disappear after the sign-out and sign-in. This is because you were using SIP Chat and not the XMPP.
Please ensure you have TCP port 5222 is allowed for XMPP Chat via Lifesize Cloud Services.