How to prevent burning when frying bread?
Given that the frying of a cube of bread is a test for oil temperature, I suspect one or both of two things are happening here -


1 The oil is not at the correct temperature when the cubes of bread are dropped in it; and 
2 The oil temperature drops when you add too many cubes in at the same time so some get burnt and some end up soggy for the single time duration you're cooking them for.


Suggested solutions -


1 Ensure the oil is at the correct temperature for the level of browness you want the cubes of bread to be fried to.
2 Don't over-crowd the pan. Fry them in batches, ensuring the oil temperature rises back to the correct one before the next batch is fried.