The Rakshasa narrative text reads "Rakshasas can withstand some degree of magic, but legends tell of blessed warriors felling them with crossbow bolts, arrows, or similar weapons" They historically have had a weakness to the Bless spell, so this is clearly carrying on that tradition. But then the stat block itself has this Damage Resistance: piercing damage from weapon wielded by creatures under the effects of the bless spell I.e., the only thing they're resistant to is the thing they're supposed to be weak to. I checked with a friend who has a hard copy and he said his book reads Damage Vulnerability, not resistance
