I have observed similar behavior after Windows has installed an important update and then rebooted the system. In my case, there appears to be a hung application that shows "starting" in the services section. I have to end the application and restart using the services tab as the configuration service, which has not started, is required to be up and running before you can log into 3CX. There is a dependency between the 3CX phone service and the 3CX phone configuration service. You might check and see if any of the dates correlate to when Windows did an update and see.
In my case,the phone system is down. I don't know that your situation is the same as mine since you indicated all else is running, which surprises me given the configuration services message.