When multiple source generators run on the same project, they do so in complete isolation from each other. In this case, both the IAspect generator and the IJobEntity generator are running without being aware of each other. But IAspect lookup in a IJobEntity relies on using a type generated by IAspect from IJobEntity. This means that the code produced by the IJobEntity generator is invalid in isolation, and this triggers a compilation error. We recently fixed some invalid compilation error detection code and a side effect was that this temporarily invalid code that somehow ended up working anyway is now completely impossible.
We're updating the documentation to reflect this change.