ArcGIS License Server Service Fails to Start

Problem

After a Windows update, I can no longer obtain ESRI licenses. The ArcGIS License Service fails to start.

Cause

The ArcGIS License Server 2018 still has stability issues (as of November 2018), which is why it is recommended to always use the license server from the same version series. For example, ArcGIS License Server 10.6.1 for ArcGIS Server/Desktop 10.6.1

Solution

Install the previous version.