diff --git a/comfy/k_diffusion/sampling.py b/comfy/k_diffusion/sampling.py
index 2d7e09838..0e2cda291 100644
--- a/comfy/k_diffusion/sampling.py
+++ b/comfy/k_diffusion/sampling.py
@@ -86,24 +86,24 @@ class BatchedBrownianTree:
     """A wrapper around torchsde.BrownianTree that enables batches of entropy."""
 
     def __init__(self, x, t0, t1, seed=None, **kwargs):
-        self.cpu_tree = True
-        if "cpu" in kwargs:
-            self.cpu_tree = kwargs.pop("cpu")
+        self.cpu_tree = kwargs.pop("cpu", True)
         t0, t1, self.sign = self.sort(t0, t1)
-        w0 = kwargs.get('w0', torch.zeros_like(x))
+        w0 = kwargs.pop('w0', None)
+        if w0 is None:
+            w0 = torch.zeros_like(x)
+        self.batched = False
         if seed is None:
-            seed = torch.randint(0, 2 ** 63 - 1, []).item()
-        self.batched = True
-        try:
-            assert len(seed) == x.shape[0]
+            seed = (torch.randint(0, 2 ** 63 - 1, ()).item(),)
+        elif isinstance(seed, (tuple, list)):
+            if len(seed) != x.shape[0]:
+                raise ValueError("Passing a list or tuple of seeds to BatchedBrownianTree requires a length matching the batch size.")
+            self.batched = True
             w0 = w0[0]
-        except TypeError:
-            seed = [seed]
-            self.batched = False
-        if self.cpu_tree:
-            self.trees = [torchsde.BrownianTree(t0.cpu(), w0.cpu(), t1.cpu(), entropy=s, **kwargs) for s in seed]
         else:
-            self.trees = [torchsde.BrownianTree(t0, w0, t1, entropy=s, **kwargs) for s in seed]
+            seed = (seed,)
+        if self.cpu_tree:
+            t0, w0, t1 = t0.detach().cpu(), w0.detach().cpu(), t1.detach().cpu()
+        self.trees = tuple(torchsde.BrownianTree(t0, w0, t1, entropy=s, **kwargs) for s in seed)
 
     @staticmethod
     def sort(a, b):
@@ -111,11 +111,10 @@ class BatchedBrownianTree:
 
     def __call__(self, t0, t1):
         t0, t1, sign = self.sort(t0, t1)
+        device, dtype = t0.device, t0.dtype
         if self.cpu_tree:
-            w = torch.stack([tree(t0.cpu().float(), t1.cpu().float()).to(t0.dtype).to(t0.device) for tree in self.trees]) * (self.sign * sign)
-        else:
-            w = torch.stack([tree(t0, t1) for tree in self.trees]) * (self.sign * sign)
-
+            t0, t1 = t0.detach().cpu().float(), t1.detach().cpu().float()
+        w = torch.stack([tree(t0, t1) for tree in self.trees]).to(device=device, dtype=dtype) * (self.sign * sign)
         return w if self.batched else w[0]
 
 
diff --git a/comfy/ldm/modules/attention.py b/comfy/ldm/modules/attention.py
index 9dd1a43c1..7437e0567 100644
--- a/comfy/ldm/modules/attention.py
+++ b/comfy/ldm/modules/attention.py
@@ -600,7 +600,8 @@ def attention_flash(q, k, v, heads, mask=None, attn_precision=None, skip_reshape
             mask = mask.unsqueeze(1)
 
     try:
-        assert mask is None
+        if mask is not None:
+            raise RuntimeError("Mask must not be set for Flash attention")
         out = flash_attn_wrapper(
             q.transpose(1, 2),
             k.transpose(1, 2),