I have a lot of problems with stability using the linuxserver/transmission docker image in my *arr stack. I setup restarting on unhealthy status in docker compose (using the following test command curl --fail http://localhost:9091 || exit 1) but even then, sometimes I just find that my donwloads have stopped and find that the container is not running at all. Do you have an alternative to suggest, which could run in docker compose?
Maybe you could just try a different Transmission docker image or build your own? Sounds like some weird instability in that particular version.