You can check docker’s service logs: journalctl -u docker -b.
If the logs provide no clues, enable debugging, restart the daemon and check the logs again: https://success.docker.com/article/how-do-i-enable-debug-logging-of-the-docker-daemon
In the past, I had trouble with corrupted log files causing a huge load on the system. Execute for log in /var/lib/docker/containers/*/*-json.log; do jq < $log 2 >&1 /dev/null || echo $log corrupted;done to check if the logfiles are still valid json. Generally make sure /var/lib/docker has plenty of free diskspace.