Please confirm you are running Veeam Backup for Microsoft Office 365 version 4c (builds 22.214.171.1241, 126.96.36.1995, 188.8.131.522) prior to installing this cumulative patch KB4099. You can check this under Help and Support > About in Veeam Backup for Microsoft Office 365 console. After upgrading, your build version will change to 184.108.40.2065.
Cumulative patch KB4099 addresses the data loss issue described in the KB4103 and includes a set of other fixes, the most significant of which are listed below:
To install the cumulative patch KB4099:
If there are any remote proxies in your environment, please update those as described here.