Thank you for the detailed description and test results.
Hosting the Active Directory Domain Controller inside a VM on the same NAS creates a boot-order timing dependency:
When the NAS powers on, TOS initializes its network and domain integration services while the Windows Server VM is still booting up. Because the DC and its DNS service are temporarily unreachable during this phase, the system's initial domain validation fails.
To help us evaluate and address this:
1.Reconnection behavior:
Once the Windows Server VM has fully booted and is responsive on the network, does simply toggling the Domain switch (disable and re-enable) in Control Panel restore the connection, or are you required to re-enter domain administrator credentials to perform a full rejoin?
2.DNS Configuration:
Ensure the NAS network interface is configured with the DC’s static IP as the primary DNS, and check if a secondary DNS server is present.
Next Step:
Please generate and download a system report via TOS Desktop > Support & Help > Issue Report and send it to support(at)terra-master.com, including a link to this forum thread. We will inspect the domain service logs and submit this scenario to our R&D team to evaluate an automated retry/reconnect mechanism for domain services when the DC is temporarily offline during boot.

