This is resolved with July 2026 Update.

The June 2026 update for SharePoint 2016, 2019, and Subscription Edition have an issue with SharePoint 2010 Workflows. We saw a similar issue with September 2024 updates (see my post here: SharePoint 2016 2019 SE – Workflows are not working after September 2024 update – Adventures of SharePoint OnPrem).

All SharePoint 2010 workflows are going to show up as Failed on Start. The ULS logs will show the following error:

06/11/2026 20:19:43.74	w3wp.exe (0x2308)	0x0E18	SharePoint Foundation	Legacy Workflow Infrastructure	66eav	High	spNoCodeXomlCompiler.IsGoodWorkflow: Potentially malicious WorkflowCodeTypeReferenceExpression: <ns2:WorkflowCodeTypeReferenceExpression QualifiedName="Microsoft.SharePoint.WorkflowActions.Helper" Type="Microsoft.SharePoint.WorkflowActions.Helper" xmlns:ns2="clr-namespace:Microsoft.SharePoint.WorkflowActions;Assembly=Microsoft.SharePoint.WorkflowActions, Version=16.0.0.0, Culture=neutral, PublicKeyToken=null" />	3ca81ca2-13ac-50de-cf2c-8aa40f51dfd5

Adding more lines to the web.config will not resolve this issue. The PG is aware and investigating this issue at this time. I will be updating this post as the investigation continues.

Description of the security update for SharePoint Server Subscription Edition: June 9, 2026 (KB5002873) – Microsoft Support

Description of the security update for SharePoint Server 2019: June 9, 2026 (KB5002874) – Microsoft Support

Description of the security update for SharePoint Server 2019 Language Pack: June 9, 2026 (KB5002876) – Microsoft Support

Description of the security update for SharePoint Server 2016: June 9, 2026 (KB5002880) – Microsoft Support

Description of the security update for SharePoint Server 2016 Language Pack: June 9, 2026 (KB5002881) – Microsoft Support