You are having an issue adding to LanGuard new computers from a second domain manually by a fully qualified domain name (FQDN), as the name gets truncated.
The root cause for such behavior is that LanGuard uses flattened domain names.
- Add a second domain following the Why Cannot LanGuard Add a Second AD or Access the Domain Controller with Dis-Joined Domain Names? article.
- Follow the best practices for using alternative credentials while managing targets from multiple domains.
Even for the computers added by FQDN, it is necessary for NetBIOS to resolve correctly to ensure successful LanGuard operations.