The odds of Rolling Bad 10xs in a Row are over 1 in 1000. The odds of rolling bad 9 times in a row are something like 1 in 800.
The odds of this sort of thing happening on a regular basis are astronomically low; assuming a 50-50 chance.

Now if it's a 20% chance, or a 25% (which is what Rapid Synthesis appears to be hitting at after many, many crafting attempts) then the odds become much more realistic.

They need to either fix it so that it actually rolls 50%; or just publish what the actual rate is so players can decide if they want to keep using it.