
Let’s go through ConfigMgr Software Updates Installation Issues Troubleshooting & Backend Process via Update Deployment Agent component (UpdateDeployment.log). I tried to give you an overview of the SCCM patching process using the Update Deployment Agent component.
Software updates in SCCM provide a set of tools and resources along with WSUS that can help to manage the task of installing Microsoft patches on Windows 10 devices. ConfigMgr also provides a solution to third-party application patching as well.
The main topic that I’m going to cover is Servicing Stack Update (SSU) software update deployment mechanism for Windows 10. You can look into other ConfigMgr logs to get a similar kind of flow for each feature. You need to configure Software Update Point (SUP) and infra setup before start using the software update feature from ConfigMgr.
TL;DR
Introduction
In this post, I assume that you already have knowledge of how to configure and deploy software updates to Windows 10 devices. You can learn more about this here -> How to Create Deploy New Software Update Patch Package Using SCCM | ConfigMgr
I have already deployed the following software updates to Windows 10 device and now the client is trying to install the updates. The following process of going through UpdateDeployment.log will help you to understand the background process. Also, this will help you to troubleshoot SCCM patching related issues.

Added to Targeted List of Deployment
This is the first step handled by Update Deployment Agent component. You can find these details in the UpdateDeployment.log.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Name (2021-01 Servicing Stack Update for Windows 10 Version 2004 for x64-based Systems (KB4598481)) ArticleID (4598481) added to the targeted list of deployment ({F7A0F5F8-689F-49BC-8EA3-966C43D8F867})
Start Downloading
The SCCM Software Update (patching) is going into Downloading state as you can UpdateDeployment.log.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateDownloading, PercentComplete = 0, Result = 0x0
Download Completed
The Configuration Manager Software Update (patching) is going into Download completed state as you can UpdateDeployment.log. The download percentage completed is 100% as per the log file.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateDownloading, PercentComplete = 100, Result = 0x0
Waiting to Install
This is the next stage for patch installation using ConfigMgr (a.k.a) and WSUS. The update goes into waiting to install stage or in the queue to get installed.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateWaitInstall, PercentComplete = 0, DownloadSize = 0, Result = 0x0
Installing
Now, the patch/software update is getting into installing stage. It also gives the indication of Percentage completed (11%) as you can in the UpdateDeployment.log.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateInstalling, PercentComplete = 11, DownloadSize = 0, Result = 0x0
Installation Completed
Let’s check how to confirm whether one patch/software update got installed successfully or installation is completed successfully. You can refer to UpdateDeployment.log and check for the key word – Progress: Status = ciStateInstalling, PercentComplete = 100, DownloadSize = 0, Result = 0x0.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateInstalling, PercentComplete = 100, DownloadSize = 0, Result = 0x0
Enforcement Message
This message in the Update Deployment log file is important. The installation (enforcement state message for installation state) was successful and Reboot pending.

Raised update (TopicID) (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) enforcement state message successfully. TopicType = STATE_TOPICTYPE_SUM_CI_ENFORCEMENT, StateId = 9, StateName = CI_ENFORCEMENT_REBOOT_PENDING, StateCriticality = 0, TopicIdVersion = 200
Soft Reboot Pending
This is the message you can see in the updatedeployment.log file to confirm whether there is any reboot pending for the patch deployment using SCCM. The key word that you can look for is Status = ciStatePendingSoftReboot.

Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStatePendingSoftReboot, PercentComplete = 0, DownloadSize = 0, Result = 0x0
Get Assignment Priority
You can also check the assignment priority for a patch or software update from UpdateDeployment.log when you are using SCCM/WSUS for the installation of patches. The keyword that you have to look into is GetAssignmentPriority. The assignment priority for SSU is #1.

GetAssignmentPriority: update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) is SSU, so that current assignment priority is 1
Successful Installation
This is the step after the restart of the Windows 10 device. The ConfigMgr patch installation got completed. The keywords are CI_ENFORCEMENT_SUCCESSFULL & Progress: Status = ciStateInstallComplete.

Raised update (TopicID) (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) enforcement state message successfully. TopicType = STATE_TOPICTYPE_SUM_CI_ENFORCEMENT, StateId = 10, StateName = CI_ENFORCEMENT_SUCCESSFULL, StateCriticality = 0, TopicIdVersion = 200
Update (Site_1074285A-82C7-474F-B242-1EE20F8C3CE5/SUM_774ec963-65e7-4c81-96e8-d229c10c3d00) Progress: Status = ciStateInstallComplete, PercentComplete = 0, DownloadSize = 0, Result = 0x0
Results
All the updates/patches will get disappeared from software center after the restart and successful installation of patches/updates.
