Again, thanks @monika , while IBM MaaS360 is a partner for Android EMM (Mobile Device Management), I'm afraid it is currently not an official ChromeOS EMM partner.
You can manage Android applications and some mobile-centric settings through the integration, but the deeper ChromeOS Device Management (which handles the device list, OS-level policies, and hardware-specific settings) requires a partner that is officially integrated with the ChromeOS Management APIs.
If your existing domain account appears to be syncing, it may be pulling in "user-level" data or legacy data that hasn't hit the API limitations yet. However, for the new customer account using the Trial Chrome Upgrade, the sync is likely returning an empty response because the management handshake between Google and MaaS360 isn't established for ChromeOS-specific device entities.
To ensure full control over your ChromeOS devices, including those on the trial upgrade, we recommend managing them natively through the Google Admin Console. This is the most robust way to enforce device and user policies, monitor device health and reporting in real-time and remotely wipe or disable lost/stolen devices.
For a list of EMM providers that are currently certified for ChromeOS policy management, you can refer to our official support page here: Manage ChromeOS devices with EMM console.