I had NOT had the "too slow to save" error message until v10 beta was installed. Now it is constant. Removing the drive and reinserting will clear it for a while, but eventually, the error comes back.
I'm using a Samsung 128 USB 3.1.
Same here. Just started getting the issue after the v10 update. On both a Samsung 128gb Fit Plus, and some random usb 3.0 micro usb adapter.