The task ran, but nothing matched the output pattern it declared
The output: declaration is a promise about filenames. If the tool wrote a different name, wrote into a subdirectory, or wrote nothing because it failed quietly, the pattern matches nothing and the workflow stops here — even though the tool itself may have exited 0.
Go to the Work dir: and simply list it: what is actually there tells you immediately whether the name differs or nothing was produced. Also check .command.err — a tool that failed but exited 0 is common, and this is where it shows up.