diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 8191c3519a36af..a78857423e7e0a 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -1067,14 +1067,9 @@ def _aggregate_frame(self, func, *args, **kwargs):
 
         result = OrderedDict()
         if axis != obj._info_axis_number:
-            try:
-                for name, data in self:
-                    fres = func(data, *args, **kwargs)
-                    result[name] = self._try_cast(fres, data)
-            except AssertionError:
-                raise
-            except Exception:
-                return self._aggregate_item_by_item(func, *args, **kwargs)
+            for name, data in self:
+                fres = func(data, *args, **kwargs)
+                result[name] = self._try_cast(fres, data)
         else:
             for name in self.indices:
                 data = self.get_group(name, obj=obj)
@@ -1441,6 +1436,7 @@ def _choose_path(self, fast_path, slow_path, group):
             raise
         except Exception:
             # Hard to know ex-ante what exceptions `fast_path` might raise
+            # TODO: no test cases get here
             return path, res
 
         # verify fast path does not change columns (and names), otherwise
diff --git a/pandas/core/groupby/ops.py b/pandas/core/groupby/ops.py
index e380cf5930f97d..fcc646dec89d9b 100644
--- a/pandas/core/groupby/ops.py
+++ b/pandas/core/groupby/ops.py
@@ -655,7 +655,15 @@ def agg_series(self, obj, func):
             return self._aggregate_series_fast(obj, func)
         except AssertionError:
             raise
-        except Exception:
+        except ValueError as err:
+            if "No result." in str(err):
+                # raised in libreduction
+                pass
+            elif "Function does not reduce" in str(err):
+                # raised in libreduction
+                pass
+            else:
+                raise
             return self._aggregate_series_pure_python(obj, func)
 
     def _aggregate_series_fast(self, obj, func):
diff --git a/pandas/core/series.py b/pandas/core/series.py
index 1039e9af929d48..ea48b3603623ac 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -1288,6 +1288,7 @@ def _set_with(self, key, value):
         else:
             if isinstance(key, tuple):
                 try:
+                    # TODO: no test cases that get here
                     self._set_values(key, value)
                 except Exception:
                     pass