Looks OK to me, docker image should be recreated.
The problem was cerated after starting the array with a missing cache device, this removed one of the devices from the pool, though the remaining device should still work assuming it was a redundant pool, but there's some issue with the superblock, I already asked LT to not allow the array to auto-start with a missing cache device, and hopefully that will be implemented soon, but for now and for anyone using a cache pool it's best to disable array auto-start, and always check every device is present before starting.
There's an issue with the remaining cache device superblock, not sure why, it's not common, a btrfs maintainer might be able to help restore it without data loss, you'd need to ask for help on IRC or the mailing list, both are mentioned on the FAQ linked earlier.