There could be several reasons why your Azure File Sync service is losing connection frequently, ensure that all necessary Windows updates are installed. For Windows Server 2012 R2, you need to have KB5021653 installed.
Check for any network connectivity problems that might be causing intermittent drops, Verify that you have the latest Azure File Sync agent version installed. Although you mentioned version 17.3, it's worth double-checking for any patches or updates.
Ensure that the Microsoft.StorageSync application has proper access to the storage account, Monitor the server's health and performance to rule out any hardware or resource issues.
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