Developer Tim Standing of SoftRAID explains a new problem in mac OS Catalina 10.15.4 in Why Is My Mac Hanging When Copying Files After Upgrading to macOS Catalina 10.15.4?.
A few days after the macOS 10.15 update was released, we began to hear of “Finder hangs” from DITs (Digital Imaging Technician) on movie sets. They were having their Macs stall when transferring hundreds of gigabytes of video from their 4K and 8K camera cards to their OWC ThunderBlades and ThunderBays. Anytime we hear about this type of problem, we immediately start looking for a cause.
A day later, we were able to reproduce the problem 100% of the time by copying 300 GB of large (10 GB) files from one SoftRAID RAID volume to another. Using a kernel debugger, we determined that the hang was not caused by an error in the SoftRAID driver. We then were able to reproduce the hang on an AppleRAID volume, using the AJA System Test Lite test application.
Once we proved the hang was not a problem with the SoftRAID driver, we alerted Apple engineers to the issue and collected further information to help them with their investigation. I can’t say when Apple will release the fix for this problem, but in the past, when they have been alerted to a hang or kernel panic, they had it resolved in the next update to macOS.
We Discovered a Temporary Work-Around for macOS 10.15.4
Once Apple releases an update to macOS 10.15, which fixes this issue, you can revert your Mac to the normal NVRAM settings and re-enable SIP.
MPG: see the blog post linked above for the work-around.
Apple’s focus on security lockdowns is creating serious problems at times. We can only hope that better testing is instituted at Apple going forward.