We are having an issues with both 'out of the box' workflows and SharePoint Designer (2010) workflows whereas after starting a workflow that includes a step to send an email, the email is not sent. This is sporadic and seems to have no rhyme or reason as to when it happens. It is failing at least %80 of the time. In the SharePoint Designer workflows, if a 1 minute pause is added to the workflow as the first action, after the pause duration the email will go out, %100 of the time.
All other email activity from SharePoint works fine. Notifications and alerts work fine. Workflows that are started via Information Management Policy work fine. It is also possible to send email via PowerShell to the exchange server (MS Exchange 2010) with a %100 success rate.
SharePoint is using Central Administration for the configuration of outgoing email, and no local instance of SMTP server is running on any SharePoint server. It has been confirmed that all SharePoint servers are allowed to send mail anonymously to our Exchange Server.
This issue started recently, after the SharePoint Security Update for Microsoft SharePoint Enterprise Server 2016 (KB4475594) was deployed on 9/28/2019.
Does anyone have an idea about how to solve this issue?