New macOS updates are causing a number of nasty problems, including bricking MacBooks.

"The April 8, 2020 Catalina 10.15.4 Supplemental Update brought my system down for several hours," said one poster on Apple's own discussion forum.

"WARNING macOS Catalina 10.15.4 Supplemental Update BRICKED my 13 inch Macbook 2018!" another user posted on the MacRumors forum.

"This has bricked my 2019 MBP. No power to the device either, needs SMC reset but it won't accept it," a third user posted." Be afraid, be very afraid. The timing could not be more brutal."

Other users reported that downloading through the App Store did not work at all.

This supplemental macOS 10.15.4 Catalina update, released on Wednesday (April 8), was intended to resolve issues created by the late March 10.15.4 update.

That earlier update caused system crashes during large file transfers, failure to wake from sleep mode, unresponsive USB-C ports, erratic restarts, and even kernel panic issues.

The new update may indeed fix them, but seems to be making things worse; do not install the Supplemental Update for Catalina 10.15.4 until Apple resolves this issue.

If you do so and your machine stops working or hangs up, one poster on the Apple discussion forum may have found a way around the problem.

"I went to recovery mode, ran Disk Utility First Aid, and rebooted again," posted tim01.