New slow file xfer Suggestions?

[jlpellet]

I have multiple TN13.0U3.1 systems & 1 has developed a slow SMB file copy that is not seen on the other systems. Whn I start a copy (from Win7) of multi-ple ~4GB files, file transfer starts at a saturated GB speed (~90+ MB/s) but over ~1 minute, it slows to10~40 MB/s. When copying to the other TN's (or a Win7 or MacOS) destinations, the copy speed start & stays at the same speed. All of the TN's are z2 single vdev <60% used. The 1 with the issue used to perform the same. The TN systems are 8GB i3, Pentium, or similar. The slow system uses 5 1TB SATA generic SSDs & the others are 6-12TB rust. I have not found any issues in logs or reports (e.g., 0 swap space used). Again, note this is a CHANGE from long-term prior performance of THIS system. Not sure what to look for but have tried the following without success.
1. Rebooted to 13.0U3
2. Replaced to network switch
3. Tried copying from a different system
3. Scrubbed the pool (no errors)

Any ideas or suggestions are appreciated.

Thanks,
John