The patch Tuesday April 2019 offered many cumulative updates for Windows 10. In a recent speech, Microsoft confirms that KB4493509 does not work on some Windows 10 v1809 PCs.
This bug is now official. The cumulative update KB4493509 for PC with the October 2018 update causes the machine to crash at start up. According to the giant, this problem only affects the machines that run the ArcaBit antivirus.
You are evaluating a patch, however the release date has not been advanced. This type of malfunction is not new. For several days it hits a lot of machines. Last week, it was discovered that the monthly totals for April 2019 for Windows 7 and Windows 8.1, as well as the associated security updates, also caused a crash at the start.
Windows 7 and 8.1, KB4493446 and KB4493472 may block some PCs, details
The reason is the presence of some antivirus. Microsoft cited Sophos security solutions but other security products like Avast and Avira are affected.
Windows 10, a boot block
If initially Microsoft didn't mention Windows 10, now it's done. The latest version of Windows, which should be more reliable and secure, is a victim of the same problem. The giant declares
"Microsoft and ArcaBit have identified a problem on devices that have ArcaBit antivirus software installed. After installing the update, the PC may not respond when restarted"
A patch is under development but, as always, no release date is announced. At the moment we are not aware of similar problems with other antivirus with Windows 10.