The tool tips say the chance to successfully reverse engineer a green item as being 20%. This is clearly rubbish. I've produced MANY MANY more greens than needed for a 1 in 5 hit rate.
I'm not sure if it's the SWTOR random number generator that's broken, or if the tool tip is wrong. Either way it should be fixed..
(and yes I know, 20% chance doesn't guarentee a 1 in 5 hit, but it should average out to that over time - and clearly, in this game it doesn't).
Just means you weren't very lucky. I remember a night when I've managed to get successful RE about 8 times out of 10 for Cybertech.
Good times. Good times....