diff --git a/modules/local/pixelator/single-cell-pna/combine_collapse/tests/main.nf.test b/modules/local/pixelator/single-cell-pna/combine_collapse/tests/main.nf.test
index 00220c34..9b55acf1 100644
--- a/modules/local/pixelator/single-cell-pna/combine_collapse/tests/main.nf.test
+++ b/modules/local/pixelator/single-cell-pna/combine_collapse/tests/main.nf.test
@@ -11,6 +11,7 @@ nextflow_process {
 
 
     test("PNA combine collapse - stub") {
+        tag "stub"
 
         options "-stub"
 
diff --git a/subworkflows/local/pna/main.nf b/subworkflows/local/pna/main.nf
index 90b37813..d6e573af 100644
--- a/subworkflows/local/pna/main.nf
+++ b/subworkflows/local/pna/main.nf
@@ -104,9 +104,9 @@ workflow PNA {
             def newMeta = data[0][0].clone()
             newMeta.remove('parts')
 
-            // Strip the duplicates meta from each element
-            def parquet = data.collect { _meta, collapsed, _reports -> collapsed }.flatten()
-            def reports = data.collect { _meta, _collapsed, reports -> reports }.flatten()
+            // Strip duplicate meta and keep a stable ordering to avoid cache misses on resume.
+            def parquet = data.collect { _meta, collapsed, _reports -> collapsed }.flatten().sort { it.toString() }
+            def reports = data.collect { _meta, _collapsed, reports -> reports }.flatten().sort { it.toString() }
             [newMeta, parquet, reports]
         }