Debugging my new network, when 10 Gigabit Ethernet Runs at 300 Megabits

I've been moving my home storage over to a UniFi UNAS Pro 8 as part of a larger homelab moderization. My main IRONHEART (the ultimate PC from a few years back) desktop now has an Intel E610-XT2 10GbE card, the NAS is on 10GbE, and there's a Minisforum MS-01 miniPC on the same network with a 10GbE SFP+ connection running Immich and Portainer and a few other things. Everything says 10 gigabit. Windows says 10 gigabit. UniFi says 10 gigabit. SMB copies are using the correct NIC but my file copies are running at around 100 to 200 megabits per second which is sad making. Naturally, I blamed the NAS, and the spinning rust within. The UNAS has six 16 TB spinning disks in RAID 6 and a pair of NVMe SSDs being used as cache. I'm also running Immich on the MS-01, with its photo library living on the UNAS, so there are lots of thumbnails, metadata reads, and little background writes happening. All seem like reasonable suspects. I switched the UNAS SSD cache from read-write to read-only. No…