Might be a bug you're experiencing or an issue with that particular weapon (I've never come across it) but in general, melee does get the sneak attack bonus. I've been one-shotting basically everything with super sledge sneak attacks for a while now.
Do u have the ninja perk? They rly dumbed down the sneak mechanics, animations... alot is missing.
Without the perk, no sneak attack.
Btw...
- no attack possible to kill silently, the finisher (not the regular attack) with a dagger thats currently possible leaves u standing up (with any sneak attack, surrounding enemies will be aware that something happend, but after that finisher u are standing, not sneaking anymore and they just aggress you)
- chained sneak kills in vats aren't working correctly either
- swords are 2-3 times more effective (daggers/knifes get the exact same multiplier)
- and even if enemies didn't fully detect you, you sometimes won't land a sneak attack, just a normal one. Quite common actually.
They only good thing is that it's not that easy anymore, ai is still stupid but alot more aware depending on light and sound.
it annoys me so much that finishes take me out of stealth.
The normal sneak attack bonus for melee weapons is 3x and pickmin's knife has a 3.5x bonus. Not really worth it if you consider that a Chinese officer sword with max upgrades does way more damage with a 3x bonus.
That explains a lot. So it max ninja it's 10.5x and thats there the extra .5 is coming from. At 10x damage another .5 is a bit silly.