Cron has no concept of paths and environment variables. I use a script and I specific rclone.conf location that I include with the script.
#!/bin/bash
# RClone Config file
RCLONE_CONFIG=/opt/rclone/rclone.conf
export RCLONE_CONFIG
#exit if running
if [[ "`pidof -x $(basename $0) -o %PPID`" ]]; then exit; fi
# Move older local files to the cloud
/usr/bin/rclone move /data/local/ gcrypt: --log-file /opt/rclone/logs/upload.log -v --exclude-from /opt/rclone/scripts/excludes --delete-empty-src-dirs --fast-list --max-transfer 700G
So you can put something in there to grab the log and see what the error is:
# Cloud Upload
12 3 * * * /opt/rclone/scripts/upload_cloud >> /tmp/test.log 2>&1