I have managed to fix an external USB-to-SATA adapter which wasn't playing well with the default usb-storage-uas driver. Yay.
The fix consisted in having the line usb-storage quirks=<VID>:<PID>:u in the /etc/modules.d/usb-storage file.
But for that to work I had to remove another quirks option which I found there... how can I define multiple quirks? 'cause, one may have multiple USB devices to setup...
Note for anyone trying to fix the same issue: VID and PID are the numbers you get with lsusb, one colon-separated pair per line right after ID, e.g. 15af:c1b8. You have to prepend 0x in the config as they are not interpreted as hexadecimal by default, e.g. e.g. 0x15af:0xc1b8.