You can also try different way of mounting Ceph FS - kernel driver vs. ceph-fuse. But definitely you do not need rclone for what you are doing - copy between two local folders (even if one is mounted other FS)
What rclone is doing according to the backtrace is checking the hash of the source and the destination match. That can take some time as it has to read the entire file to hash it.
If you don't want this then try --size-only or --update
About 1-2 gigabytes
Rclone show checking message endlessly but if i run command lsof -p $rclone_pid then rclone start working and successfully completed