Fauxreigner

Had the same issue. node-red-contrib-actionflows is causing a failure. To fix, edit your nodered docker template and set safe mode (Container Variable: NODE_RED_ENABLE_SAFE_MODE) to true. This will allow NodeRed to start, but not load or run flows, which stops the crash. Then, you can connect to the NodeRed UI, click the menu (three lines) at the top right, select Manage palette, and update node-red-contrib-actionflows (and anything else you want to update). Then, stop the container, set safe mode to false, and start the container. Should start up normally.

So, the bad news is, that's a bad assumption. I never installed the rc versions and went straight from 6.3.5 to 6.4, and ended up having the black screen issue. The good news is, deleting the container and its appdata folder and reinstalling fixed it, so wiping out the docker.img wasn't required.