Different behavior of FTDI USB RS485 on different computers
I encountered exactly the same problem: FTDI based USB&lt;>RS485 converter (brand is "DIGITUS"), running at 57600bps, working on some machines properly and on some it send bigger chunks of data very very unreliable.
What I found out (after wasting lots of time of investigations on grounding and bus termination), is that on fast machines it did not work, because the RS485 driver chip (not made by FTDI) did not release the RS485-bus fast/reliable enough in relation with the output of the FTDI chip. FTDI is releasing the bus after each and every byte (right after the stopbit) via the TXEN port and acquires it immeditately again for the next byte (which on fast machines is already in the buffer).
The workaround was, to put a delay between every sent byte and it worked. Yes, pretty bad workaround. Wish FTDI would give an option e.g. in the driver to adjust the TXEN timing.