When a Teams chat is started it automatically creates a Exchange group mailbox, an OneDrive account for that same group mailbox and a SharePoint site for that Teams chat. All conversations are put in the Exchange group mailbox and up until October 2020 they could be found under the folder Conversation History\Team Chat. Now here comes the fun part, starting October Microsoft changed something in how they save the chats and they moved the chats to a new folder named ~TeamsMessagesData.
During the roll-out of a M365 customer we encountered that the teams chats were not being backupped past September 2020 and as I could not find any issue with the back-up nor any configuration issues we opened a case with Commvault to research the issue. Big was our surprise as in the first reaction from the Commvault engineer I received the answer to my question, namely a hidden additional setting which would enabled the back-up of the new Teams chat folder, being:
Location = HKLM\SOFTWARE\Commvault Systems\Galaxy\Instance001\MSExchangeMBAgent
Value = 1
The additional setting should be set on all mailbox proxies/access nodes and will add the new folder named ~TeamsMessagesData to the back-up, which in our case it also did.
Upon further questioning the Commvault engineer why this was not shared in BOL we got the answer that as it was only occurring since October 2020 and it has been fixed in FR22 they were not going to publish this on BOL and would only share this on a case by case base.
Now for all of you out there, If you have any customers running M365 backups and which are not planning to update to FR22 in the foreseeable future please be aware of this setting and maybe proactively share/apply this setting as to prevent any dataloss for Teams chats.
And to Commvault, please be open about this and communicate to partners at least!