Have you seen this scenario before?
You set up a workflow to make changes via PowerShell. This is via a PS script that resides locally on the Server. You also setup MPR to trigger the workflow.
You make changes to an object to trigger the MPR, look in the logs and you see the MPR is triggered but there are no changes from the workflow. You even enable some sort of logging on your workflow but you see that the PS script is not triggered. Sometimes it fires off, and other times it does not.
It is very likely you have more than one MIM Service server. Quite a lot of people forget to apply updates to both servers especially where it involves PS scripts and new dlls. I always recommend running your PS scripts internally rather than externally that way if you don’t have to copy the PS script to the second server. But that does not always resolve it. if you have any new dlls to be installed remember to install it on both servers.
Your workflow can be processed by either MIM server so they must be kept in identical settings all the time. I recommend DFS to sync folders between the servers. Does not resolve installation of libraries and registry updates, which still has to done manually on the servers.