It's good you got it to work.
I tried to replicate your setup, and it seems to work without a splitter as well:
Both of the gates are taking the same point on the output belt as source. The output belt is at 2x speed, the porcelain belt is at 1x speed and the starch belt is at 3x speed. I ran the setup for 100 recipes, and it didn't seem to jam for me.
Btw, congratulations on automating nuclear fuel!