I see two potential issues:
2022-10-14 16:33:08 ERROR : sftp://root@10.5.17.74:22//NL10/: Discarding closed SSH connection: read tcp 10.200.7.117:46182->10.5.17.74:22: i/o timeout
2022-10-14 16:33:08 ERROR : sftp://root@10.5.17.74:22//NL10/: Discarding closed SSH connection: read tcp 10.200.7.117:46178->10.5.17.74:22: i/o timeout
2022-10-14 16:33:08 ERROR : sftp://root@10.5.17.74:22//NL10/: Discarding closed SSH connection: read tcp 10.200.7.117:46180->10.5.17.74:22: i/o timeout
These are actually DEBUG messages and not really ERRORs. They just tell that rclone is taking some unused and expired SFTP connections out the the connection pool.
This process however isn't 100% robust (there is a potential race condition), so these messages are best to avoid or keep at a minimum.
I guess it happens because your sync starts out by using all the available --checkers (default is 8), which takes an SFTP connection each. Later the when the checks are finished the connections are no longer needed and start to fall out of the pool as the SFTP server cleans up the unused connections. I see this on my Synology.
You can probably work around this by lowering --checkers. I think --checkers=2 would be fine when you have --transfers=1.
The SSH_FX-FAILURE is a broad message from the SFTP server that basically means that you cannot create a file (at the given location). This is typically due to missing access rights or out of disk space.
Here are a few recent threads with hints:
https://forum.rclone.org/t/ssh-fx-failure-for-normal-usage/32836
https://forum.rclone.org/t/error-with-sftp-remote-mkdir/33499