For some reason, the Kodi-based NFS was using a very small block size:
NFS: chunks: r/w 8192/8192
8K will be very inefficient and might have contributed to your problem. Last time I looked, Kodi-based mounts were using block sizes up to 500K, eg 2 x Vero 4k not recovering from dim (screensaver) - #18 by decepticlone
A kernel-based mount should hopefully choose a larger block size, as well as generally being more efficient.