Workflow was cancelled by System Account. Workflow failed to start

It looks like you are also experiencing workflow issues after updating for SharePoint Server 2016.

You might experience an issue in which SharePoint workflows can’t be restated because the unauthorized type is blocked. The issue also generates event tag “c42q0” in SharePoint Unified Logging System (ULS) logs.

To work around this issue, register the safe types in the Web.config file. You can look for event tag “c42q0” in ULS logs to find the blocked type. If the type and assembly are safe, add the type to the authorized list in the Web.config file.

For example:

<System.Workflow.ComponentModel.WorkflowCompiler>
   <authorizedTypes>
     <targetFx version="v4.0">
        <authorizedType Assembly="Microsoft.SharePoint.WorkflowActions, Version=16.0.0.0, Culture=neutral, PublicKeyToken=null" Namespace="Microsoft.SharePoint.WorkflowActions.WithKey" TypeName="*" Authorized="True" />
    </targetFx>
   </authorizedTypes>

Reference:

https://blog.stefan-gossner.com/2024/09/13/trending-issue-problems-with-workflows-after-applying-september-2024-cu-for-sharepoint-2016-2019-se/

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Today I started getting following error:

Potentially malicious xoml node: <ns2:BuildAssignmentsXmlActivity __Context="{ActivityBind ROOT,Path=__context}" Value="&lt;my:Assignments xmlns:my=&quot;http://schemas.microsoft.com/office/infopath/2003/myXSD&quot; xmlns:pc=&quot;http://schemas.microsoft.com/office/infopath/2007/PartnerControls&quot;&gt;&lt;my:Assignment&gt;&lt;my:Assignee&gt;&lt;pc:Person&gt;&lt;pc:DisplayName/&gt;&lt;pc:AccountType/&gt;&lt;pc:AccountId&gt;[%ID4522.ReturnValue%]&lt;/pc:AccountId&gt;&lt;/pc:Person&gt;&lt;/my:Assignee&gt;&lt;my:Stage&gt;0&lt;/my:Stage&gt;&lt;my:AssignmentType&gt;Serial&lt;/my:AssignmentType&gt;&lt;/my:Assignment&gt;&lt;/my:Assignments&gt;" ReturnValue="{x:Null}" x:Name="ID4521" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ns2="clr-namespace:Microsoft.Office.Workflow.Actions;Assembly=Microsoft.Office.Workflow.Actions, Version=16.0.0.0, Culture=neutral, PublicKeyToken=null" />

Added following entry in web.config, restarted timer job, restarted workflow but same issue.

<authorizedType Assembly="Microsoft.Office.Workflow.Actions, Version=16.0.0.0, Culture=neutral, PublicKeyToken=null" Namespace="Microsoft.Office.Workflow.Actions" TypeName="*" Authorized="True" />