Microsoft has introduced a change in Office licence enforcement.
In the past, once Office was activated after installation, the software would work fully in perpetuity. There were no ongoing licence checks. Even if you bought a pirated or illegal licence, once it was activated, Office would continue to work even if Microsoft cancelled the licence.
Software activation or authorisation is now an ongoing process. From time to time, Office 2019 and Office 365 checks with Microsoft to ensure the software can be legally used. Office 2019, using ‘Click to Run’ installation, allows Microsoft to deactivate an illegally licensed install of Office at any time in the future.