Out of drive space.
Have Sonarr running for about a month or so. I manually delete files when no longer wanted, so in theory there should be PLENTY of drive space.
I check the repository for Transmission, check any local locations and deleted plenty of file, yet drive still stating no space left. Does Sonarr (or docker) create a private or hidden copy of files as well by chance?
MacMini / 10.15.4 Catalina / Docke + Sonarr