diff --git a/timm/models/vision_transformer_packed.py b/timm/models/vision_transformer_packed.py
index c2f71f94ba..efda484f90 100644
--- a/timm/models/vision_transformer_packed.py
+++ b/timm/models/vision_transformer_packed.py
@@ -230,7 +230,8 @@ def forward(self, x, attn_mask: Optional[torch.Tensor] = None):
         else:
             q = q * self.scale
             attn = q @ k.transpose(-2, -1)
-            attn += attn_mask
+            if attn_mask is not None:
+                attn += attn_mask
             attn = attn.softmax(dim=-1)
             attn = self.attn_drop(attn)
             x = attn @ v
@@ -292,7 +293,7 @@ def __init__(
         self.ls2 = LayerScale(dim, init_values=init_values) if init_values else nn.Identity()
         self.drop_path2 = DropPath(drop_path) if drop_path > 0. else nn.Identity()
 
-    def forward(self, x, attn_mask: Optional[torch.Tensor]):
+    def forward(self, x, attn_mask: Optional[torch.Tensor] = None):
         x = x + self.drop_path1(self.ls1(self.attn(self.norm1(x), attn_mask=attn_mask)))
         x = x + self.drop_path2(self.ls2(self.mlp(self.norm2(x))))
         return x
@@ -720,8 +721,11 @@ def forward_features(
 
         if attn_mask is None:
             attn_mask = seq_ids.unsqueeze(2) == seq_ids.unsqueeze(1)
-            key_padding_mask = (seq_ids != 0).unsqueeze(1)
-            attn_mask = attn_mask & key_padding_mask
+            # NOTE: not applying key padding mask as padding tokens are already isolated to
+            # themselves via the above mask (padding has seq_id == 0). Doing an additional
+            # key padding mask results in fully masked rows which causes numerical issues.
+            # key_padding_mask = (seq_ids != 0).unsqueeze(1)
+            # attn_mask = attn_mask & key_padding_mask
             attn_mask = attn_mask.unsqueeze(1)
 
         if attn_mask.dtype == torch.bool:
@@ -729,11 +733,12 @@ def forward_features(
             min_val = torch.finfo(dtype).min
             attn_mask = torch.zeros_like(attn_mask, dtype=dtype).masked_fill_(~attn_mask, min_val)
 
-        # if self.grad_checkpointing and not torch.jit.is_scripting():
-        #     tokens = checkpoint_seq(self.blocks, tokens)
-        # else:
         for b in self.blocks:
-            tokens = b(tokens, attn_mask=attn_mask)
+            if self.grad_checkpointing and not torch.jit.is_scripting():
+                tokens = torch.utils.checkpoint.checkpoint(
+                    b, tokens, use_reentrant=False, attn_mask=attn_mask)
+            else:
+                tokens = b(tokens, attn_mask=attn_mask)
         tokens = self.norm(tokens)
 
         device = tokens.device
@@ -743,7 +748,7 @@ def forward_features(
         seq_lens = seq_lens.reshape(-1)
         valid_rows = seq_lens > 0
         if self.attn_pool is not None:
-            unpack_mask = unpack_mask & key_padding_mask
+            # unpack_mask = unpack_mask & key_padding_mask
             unpack_mask = unpack_mask.unsqueeze(1)
             unpack_mask = torch.zeros_like(unpack_mask, dtype=tokens.dtype).masked_fill_(
                 ~unpack_mask, torch.finfo(tokens.dtype).min)
@@ -767,6 +772,7 @@ def forward_head(self, x, pre_logits: bool = False):
             if isinstance(x, (list, tuple)):
                 x = torch.stack([t.mean(dim=0) for t in x], 0)
             else:
+                # x = x.sum(dim=1) / seq_lens.reshape(-1, 1)
                 x = x.mean(dim=1)
         x = self.fc_norm(x)
         x = self.head_drop(x)
@@ -801,6 +807,7 @@ def _cfg(url='', **kwargs):
 
 
 default_cfgs = generate_default_cfgs({
+    'navit_medium_patch16_384': _cfg(),
     'navit_base_patch32_224': _cfg(),
     'navit_base_patch32_384': _cfg(),
     'navit_base_patch16_224': _cfg(),
@@ -821,6 +828,16 @@ def _create_vision_transformer_packed(variant, pretrained=False, **kwargs):
     )
 
 
+@register_model
+def navit_medium_patch16_384(pretrained=False, **kwargs) -> VisionTransformerPacked:
+    model_args = dict(
+        img_size=384, patch_size=16, embed_dim=512, depth=12, num_heads=8,
+        fc_norm=False, init_values=1e-5, qkv_bias=False)
+    model = _create_vision_transformer_packed(
+        'navit_medium_patch16_384', pretrained=pretrained, **dict(model_args, **kwargs))
+    return model
+
+
 @register_model
 def navit_base_patch32_224(pretrained=False, **kwargs) -> VisionTransformerPacked:
     model_args = dict(patch_size=32, embed_dim=768, depth=12, num_heads=12)