The following is one of the reports:
Environment: Pro Workstation running version 1909 on a Domain network.
This KB4549951 update slows down networking. Outlook 365 on the hosted Exchange took several minutes to load and froze. Remote Desktop had a black screen on the destination computers. This update also causes the VM software to freeze. Everything continued to work normally after uninstalling and postponing the updates for 30 days.
Some people also report that this update deletes files. For affected people, their files were moved or deleted after the update. Users report that after the update was installed, their settings disappeared, and their personal files were moved to the Recycle Bin or simply deleted all at once.
Interestingly, on some systems, updating me does not delete files or settings. It just can not be installed or, when finally installed, causes BSoDs, with the following errors PAGE_FAULT_IN_NONPAGED_AREA, CRITICAL_PROCESS_DIED, ACPI_BIOS_ERROR, INACCESSIBLE BOOT DEVICE, MEMORY_MANAWATION_.
Finally, for some users, the update greatly affects the performance of their operating system and causes connectivity problems.
Microsoft has not yet identified the problems so far. If the update has problems on your computer, you can uninstall it manually.