I have searched and searched for a solution, but no luck

I have a simple on/off sequence created on Vixen, and exported it to run on FPP, and it appears to work fine.
If I replace the on/off functions with a ramp, twinkle, ect. the data seems to be corrupted going to the Renard controllers.
The more complex the sequence, the worse the corruption seems to be.
If I move the RS485 from the Pi to the computer, the sequence runs correctly.
Using the test function in FPP, everything works as expected.
I have killed all software on the PC, so there should not be any interference on the wifi into the Pi (seems others have been bit by this) - I don't have any inputs enabled anyway on FPP.

Details:
Vixen 3.5u4
Pi B+ running latest version of FPP, using recommended 2.5A power adapter.
RS485 dongle (DSD TECH SH-U10 USB to RS485 Converter with CP2102 Chip)
connected directly to Pi, going to two Renard TR8 controllers in series (16 channels).
Cat 5 cable is used, ~3' Pi to first controller, and 10' between them to the second one.
I have tried both termination and unterminated at the Renards, no difference.
The yellow framing light never blinks.

I am currently waiting on a powered hub, thinking there could be insufficient voltage at the USB port.
Also planning on building a similar test sequence on xlights, but not had the time to do that yet.

Any other ideas?