Disappearing docker container

[DACN]

Installed docker-transmission-openvpn on my rpi 4 for the first time about two weeks ago. This was on top of a fresh install 64 bit raspberry pi version of debian with a fresh install of jellyfin. Successfully used it quite a few times to pull down files. Was away all last week, and came home to find

1. rpi still running, and
2. no transmission gui

Looking further - the container seems to have completely disappeared. When I do

docker container ls -a

I can only see three (!) instances of docker hello-world containers. Can't spot anything in the logs.

The only other thought which may/may not be relevant. While 64 bit rpi4 has just enough legs to transcode hevc/265 to my roku stick - that seems to be it maxed out. So, for the period while I was away I had left a python script running which

1. crawled my library
2. identified h265 files (using a call to ffprobe)
3. recoded them to h265 (using a call to ffmpeg)

But that job did seem to have stalled. So, before I re-install. Any thoughts as to what might have happened?