diff --git a/pipeline/01-train.R b/pipeline/01-train.R
index c9cc5237..73387c61 100644
--- a/pipeline/01-train.R
+++ b/pipeline/01-train.R
@@ -318,6 +318,12 @@ if (cv_enable) {
   # CV iteration
   lgbm_search %>%
     lightsnip::axe_tune_data() %>%
+    # Drop the trace column tune attaches to each nested .notes tibble: it
+    # holds rlang stack objects that arrow cannot serialize
+    mutate(.notes = purrr::map(
+      .notes,
+      ~ dplyr::select(.x, -dplyr::any_of("trace"))
+    )) %>%
     arrow::write_parquet(paths$output$parameter_raw$local)
 
   # Save the parameter ranges searched while tuning
diff --git a/pipeline/06-upload.R b/pipeline/06-upload.R
index 5f7e1761..ebcc2ff1 100644
--- a/pipeline/06-upload.R
+++ b/pipeline/06-upload.R
@@ -95,10 +95,23 @@ if (upload_enable) {
       read_parquet(paths$output$parameter_raw$local) %>%
         tidyr::unnest(cols = .metrics) %>%
         mutate(run_id = !!run_id) %>%
+        # Each model fit can leave a warning in .notes, but notes don't
+        # record which config produced them. At .iter = 0 each fold holds
+        # all initial configs, so joining the notes unnested would attach
+        # every warning to every metrics row for that fold. Collapse notes
+        # to one row per fold and iteration first so the join can't
+        # multiply rows
         left_join(
-          rename(., notes = .notes) %>%
-            tidyr::unnest(cols = notes) %>%
-            rename(notes = note)
+          select(., id, .iter, .notes) %>%
+            tidyr::unnest(cols = .notes) %>%
+            group_by(id, .iter) %>%
+            summarize(
+              location = paste(unique(location), collapse = "; "),
+              type = paste(unique(type), collapse = "; "),
+              notes = paste(unique(note), collapse = "; "),
+              .groups = "drop"
+            ),
+          by = c("id", ".iter")
         ) %>%
         select(-.notes) %>%
         rename_with(~ gsub("^\\.", "", .x)) %>%