Hi Samwise,
I'm not sure I fully understood your use case but one thing that did not sound right to me was this part:
"The assembly containing the services factory is on another maintenance unit.
...
The assembly and service factory are configured on each maintenance unit and workspace as shown: MyAssembly.WsasFactory"
If you have a Maintenance Unit called MU_1 with an Assembly named "MyAssembly" that contains a Service Factory type file named "WsasFactory" and this Service Factory should apply at Workpace level (across all MUs) then you should only be configuring it at the WS level (i.e.: Workspace Assembly Service = MyAssembly.WsasFactory).
You should not be assigning this Service Factory to a different Maintenance Unit as that assembly will not exist there and I'd expect it to result in an error.
If I understood it right and this mirrors you current set up I'd start by leaving the Workspace Assembly Service setting blank at MU level and only configure it at Workspace level and try again.
If this is not your case apologies for the confusion and you might want to share some print screens of your config and code so we can try and help further.
