On clients, where the Folder Encryption module is used, the Windows 10 Update, build 1809 cannot be carried out.
On the client, there is user data encrypted with Folder Encryption. The access to encrypted data is granted only to the owner of the used encryption key. During the Windows Update 1809, a system process, which doesn't have an encryption key, tries to open the encrypted data. Folder encryption then denies access. The Windows Update stops.
The access to user data because of October 2018 Update 1809 caused many other interrelated problems, which is the reason why the release was initially postponed. On 13.11.2018, Microsoft announced that it will provide the Update little by little.
Check how the Windows Update deployment is configured in your environment and disable updates temporarily.
Microsoft offers the following Show or hide updates troubleshooter package: