Sometimes Rop Mantra Top seems to need to have everything upstream cooked before it can cook successfully. So I dirty and run the entire network, it fails at the ROP, then I wait, run it again and then it works.
Is that other people experience too?

After the ROP I have an Overlaytext Top and that is failing because the @pdg_input does not seem to work in the pdg_result filefetch cop node. I changed the @pdg_input to something like CUsers///Tops/render/city.ropmantra`@wedgenum`.exr and then it worked.
When I middleclick on a work item in the cooked ROP it says “Expected Output” but not “Output”. But the renders are done and the ROP says “Finished” (without errors).
Could this be a user error of some kind?

Could you please post your file? We'll take a look.