RN516 USB3 stability problems(many I/O errors) and other issues

Hello to all.
From the beginning we have been using an RN516 as a target for our Veeam backup with good results because it is fast enough. However, we need to copy those archives in an external USB disk for security reasons and we programmed that operation with its own NAS backup procedure: if we use USB3 disk we get through stability problems (see attached image).

We noticed that only the first attempt is successfull and with the second one,  errors arise and  than  we have to restart the NAS because USB ports goes down and at that point it is not able any more to recognise a new disk connected to it.
We made several tests:
1)we changed the cable with a quality one;
2)for testing we used a seagate external disk an other 2 different external case (ASM chipset).
The strange thing is that the procedure shows to be pretty rock stable if we use a USB2 disk.
I have also a curiosity: is it correct that every time I connect and  disconnect a USB disk  ,in my Esxi log I see the warning  “All Paths Down state"  that last 7 seconds? At the same time, the NAS log shows that NFS protocol stops and restarts.
Thank you in advance for your help.