Because the bleed for swordsman never worked properly before.
Bleed with thrust on a stunned enemy works, if that’s what you mean.
The bleed proc from thrust works but either, it doesn’t work with restrain or the stun is too short for restain to work with thrust.
Everything works, it’s just Restrain that’s broken.
You can see why very easily. Use any stun, any stun at all, and then stun with Restrain. Different debuffs. They’re just both called Stun and do exactly the same thing, except the Restrain version doesn’t work with any other stun related effects.