Make sure you’re using a recommended 1394b card. FW400 out of the MR to FW800 port on the pcie card. Also make sure you’ve selected the Legacy Firewire driver. Def do a full uninstall and reinstall of latest drivers etc. I could also get down to 32 samples without any issues on windows 10 x64 1809. I now use my MR units as slaves so sadly cannot offer more input