I had the same problem on 3 machines. All of them were Win 10 x64 1903 with latest fixes. Two of them use ESET NOD32 12.2.29.0 one uses McAfee. All the machines run Win 10 1903 with latest fixes and all of them reported that Defender and the installed AV (ESET or McAfee) were disabled at startup. So I think itman gave the right hint to what is happening.
In my case I looked at the Services. The blue box including the red box shows how it looks like when everything works. In my case the problem was caused by the service in the red box that had Status running and the Startup Type was set to Automatic. I have no idea when it happened and how it came to this.
While trying to fix the problem I used a small program to view and change some settings of Windows. If anyone is interested in this program you can get it here for free https://www.oo-software.com/en/shutup10
The section Windows Defender and Microsoft SpyNet is the one I was interested in. The red box shows how it should correctly be set. In my case the switch showed green color and was set to the right (like the above switches). I switched it back to what is shown in the red box and performed a shutdown and power on. The services then looked like above and the message did no longer come up.
I did this change a few days ago to make sure it works at least for me bevor posting what I did. Maybe this might help someone, at least it could give a hint to someone who is more knowledgeable than me. There also should be a setting somewhere in Windows that does what the program does but I don't know where. If anyone knows where to find it there is no need to use the program.
