Microsoft has released a hotfix that fixes multiple issues including the most annoying that I used to see at my customers very frequently.
In SharePoint Server 2013 and later versions, if you edit a workflow or update an email template by using the FIM Portal, the version is automatically updated to 18.104.22.168. This causes a system error message during processing.
In a nutshell: if you change or create a new MIM workflow and put a standard MIM workflow activity there (like Owner Approval Workflow, Password Reset Action Workflow etc..), the workflow XOML definition would contain references to .Net version 22.214.171.124. This broke the workflow completely as the default .Net version for the standard activities is 126.96.36.199. In the request log you would see failed requests with the error description “Unable To Create New WorkflowInstance For WorkflowDefinition”.