docker images and containers disappearing without use of --rm

[elanstop]

Hi there, I've followed all the instructions for running a local blast search within a GCP vm instance on the suggested hardware. Trying to follow the instructions for using bind mounts did not work for me, as needed files remained unavailable to the container. I also preferred to keep the containers, so I used docker cp to transfer the files instead, dropped the --rm flag, and otherwise modified the commands for execution from within the container. This all works fine. The problem is that after a day or two, the image and stopped container inexplicably disappear from the vm (at least according to the results of docker ps -a and docker images ls), and I lose a bunch of work. They do, however, persist across reboots. I'm very confused by this problem and any help would be much appreciated.