Hello, I believe there are two documents that can help explain this behavior and offer a few potential solutions:
This document describes the root cause of the drift you are most likely seeing. The default installation on your target will include NI-DAQmx and NI-Sync, the latter of which includes some services that will steer the clock.
One option to disable that behavior is described in this document. If you install NI-Sync 20.1 to the target (not sure which version you currently install), you can disable the described behavior. At that point, you should be able to synchronize as expected.
One potential other option: if you do not need NI-Sync installed, you could uninstall it. Off the top of my head, I am not certain of the dependency relationships and how that might impact other installed software (e.g. NI-DAQmx).
In either case, I would be interested in hearing more about your application and what you are trying to accomplish so we (NI) can evaluate how we can better serve this type of use case. Please feel free to send me a message.