The process was killed from outside for using too much memory
137 is 128 + 9, meaning SIGKILL. In practice that is nearly always the kernel's OOM killer or a container/scheduler memory limit — not a bug in your data or command. The tool's own output explains nothing because it was never given the chance.
Raise the memory for that specific step rather than the whole run: the memory directive for that Nextflow process, resources: mem_mb in Snakemake, --memory for Docker, or your scheduler's request. If it dies at the same input regardless of the limit, look at what is unusual about that input.