ensure explicit eval_sample_packing to avoid mismatch issues (#1692)

src/axolotl/utils/config/models/input/v0_4_1/__init__.py

@@ -899,6 +899,15 @@ class AxolotlInputConfig(
             raise ValueError(
                 "eval_table_size and eval_sample_packing are not supported together with sample_packing. Please set 'eval_sample_packing' to false."
             )
+        if (
+            data.get("sample_packing")
+            and data.get("eval_sample_packing") is None
+            and not data.get("eval_table_size")
+        ):
+            LOG.info(
+                "explicitly setting `eval_sample_packing` to match `sample_packing`"
+            )
+            data["eval_sample_packing"] = True
         return data
 
     @model_validator(mode="before")