These behaviors are expected and are due to current product limitations rather than sandbox-specific issues.
The first issue occurs when a Trigger Merge uses a Multi-Step Report (MSR) as a sublist report. Although the error message indicates that the user does not have a Multi-Step Report license, the actual cause is that Trigger Merge currently does not support MSRs as sublist data sources. This is a known product limitation, and the licensing message is misleading. Support for MSRs as sublist reports has been raised as a potential enhancement.
The second issue occurs when an unlicensed user updates a record that initiates the Trigger Merge. Trigger Merge executes in the context of the user performing the record update and relies on that user's Apsona metadata during execution. If the initiating user does not have an active Apsona license, the required metadata cannot be retrieved, causing the merge to fail with a "Can't find metadata" error.
To avoid this issue, ensure that any user who may trigger the Flow has an active Apsona license. If Trigger Merge fails with a licensing error while using an MSR as a sublist, remember that the root cause is the current lack of support for MSRs in Trigger Merge rather than an actual licensing problem.