We are having the same problems with about 200 Windows 10 build 1903 systems that upgraded to version 14.2.4814.1101. We halted the upgrade process after that so that our remainig 2000 systems are still on version 14.2.4811.1100 (which seems OK).
We logged a case with Symantec and have downloaded logs as well. Case 30451676
What conditions cause the SEP client problem? It appears that it takes a combination of things to have the problem:
1. You must be running Windows 10 build 1903 that has been upgraded from at least one or more previous Windows 10 builds. A fresh install of Windows 10 build 1903 seems to be OK.
2. You must either upgrade or do a fresh install of the latest SEP client (i.e. version 14.2.4814.1101). Installation of previous builds of the SEP client are OK.
3. Our other OS's (Window 7 and Windows Server 2012 R2) are not affected by this problem.
What problems do we see?
1. Applications like MMC.EXE or any application that uses MMC (like Event Viewer or Services) fails to start with a message that says: This application has been blocked for your protection.
2. The SEP client cannot be uninstalled or re-installed without error. From what I can tell, the Teefer service (i.e. the firewall link into the OS) fails to uninstall or reinstall.
3. Even after using CleanWipe to remove the SEP client, the problems still exist. This indicates that the SEP client was not fully removed or changes made to the OS were not fully reverted.
4. Other applications may also fail to install or update. For example, I tried to do a nVidia driver update which failed.
5. There are numerous errors in both the Application and System event logs that are not normally there if the system is operating normally. I am not sure how much this affects system performance, but it can’t be good.
6. I suspect there are other issues, but those are the ones I have seen and can replicate.
I hope Symantec can find a fix soon, or we will be rebuilding a lot of systems.