IGB with HLC gets 4 hits against Biggs. Biggs rolls one evade which gets crackshotted (by IGB). Can R4-D6 be used to cancel two hits (which will give Biggs 2 stress)?

Long answer:

R4 D6:

When you are hit by an attack and there are at least 3 uncancelled [Hit] results, you may choose and cancel those results until there are 2 remaining. For each result cancelled in this way, receive 1 stress token.

Crackshot:

When attacking a ship inside your firing arc, you may discard this card to cancel 1 of the defender's [evade] results.

The clue is in the first line of R4 D6 - "When you are hit by an attack" - a Hit is determined when there are uncancelled dice results after all dice have been rolled, the results compared hit / crit results cancelled, and before damage has been dealt - so that's when R4 triggers.

Crackshot happens during the cancel dice step - after all dice have been rolled and modified and evade tokens spent but before the other steps listed above.

so R4 triggers after Crackshot.

Short answer:

Yes