Let’s look at the entire pool to rule out some things:
zfs list -t fs -r -o name,encroot,encryption,keyformat,keylocation <pool> | grep -v "\.system"
The history of the pool can provide clues on what happened:
zpool history <pool> | tail -n 100
You will have to copy the output from some day before the date that this started.
Please don’t post the output as a screenshot and please use preformatted text.