diff --git a/.github/workflows/mcstas-conda-testsuite.yml b/.github/workflows/mcstas-conda-testsuite.yml
index 629e2cf7c..d27ac04dd 100644
--- a/.github/workflows/mcstas-conda-testsuite.yml
+++ b/.github/workflows/mcstas-conda-testsuite.yml
@@ -107,8 +107,7 @@ jobs:
              export TMPDIR=${HOME}/tmp
            fi
            # Run the test with 2 core mpi
-           ${MCTEST_EXECUTABLE} --verbose --testdir $PWD --suffix ${{ matrix.os }}_${{ matrix.mpi }} --mpi=2
-
+           ${MCTEST_EXECUTABLE} --verbose --testdir $PWD --suffix ${{ matrix.os }}_${{ matrix.mpi }} --mpi=auto
     - name: 'Tar output files'
       id: tar-package
       if: always()
@@ -200,31 +199,33 @@ jobs:
            for tgz in downloaded_artifacts/*/*.tgz; do
              work=$(mktemp -d)
              tar xzf "$tgz" -C "$work"
-             mv "$work"/run_test-suite/* mcstas-nightly/
-
-             # Linux (ubuntu-latest) is the reference platform; the label
-             # name itself embeds a version string and timestamp we can't
-             # predict, so identify it via the source artifact/tarball name
-             # instead of hardcoding it.
-             if [[ "$tgz" == *"ubuntu-latest"* ]]; then
-               REFLABEL=$(basename "$labeldir")
-             fi
+             artifact_name=$(basename "$(dirname "$tgz")")
+
+             for labeldir in "$work"/run_test-suite/*/; do
+               if [[ "$artifact_name" == *"ubuntu-latest"* ]]; then
+                 REFLABEL=$(basename "$labeldir")
+               fi
+               mv $labeldir mcstas-nightly/
+               done
+             done
              rm -rf "$work"
-           done
 
            if [ -z "$REFLABEL" ]; then
-             echo "ERROR: could not identify the Linux/reference column (ubuntu-latest artifact missing?)"
-             exit 1
+             echo "WARNING: could not identify the ubuntu-latest/conda reference column"
+           else
+             echo "REFLABEL=$REFLABEL" >> "$GITHUB_ENV"
+             echo "Reference column: $REFLABEL"
            fi
 
-           echo "REFLABEL=$REFLABEL" >> "$GITHUB_ENV"
-           echo "Reference column: $REFLABEL"
-           ls mcstas-nightly
-
     - name: 'Run mcviewtest across all platform columns'
       id: viewtest
       run: |
-           cd "$PWD/mcstas-nightly" && mcviewtest --reflabel "$REFLABEL" --nobrowse
+           cd "$PWD/mcstas-nightly"
+           if [ -z "$REFLABEL" ]; then
+             mcviewtest --reflabel "$REFLABEL" --nobrowse
+           else
+             mcviewtest --reflabel --nobrowse
+           fi
 
     - name: 'Tar mcstas-nightly output (all platform folders + comparison table)'
       id: tar-package
diff --git a/.github/workflows/mcxtrace-conda-testsuite.yml b/.github/workflows/mcxtrace-conda-testsuite.yml
index ff0247e77..bce716a2e 100644
--- a/.github/workflows/mcxtrace-conda-testsuite.yml
+++ b/.github/workflows/mcxtrace-conda-testsuite.yml
@@ -107,7 +107,7 @@ jobs:
              export TMPDIR=${HOME}/tmp
            fi
            # Run the test with 2 core mpi
-           ${MXTEST_EXECUTABLE} --verbose --testdir $PWD --suffix ${{ matrix.os }}_${{ matrix.mpi }} --mpi=2
+           ${MXTEST_EXECUTABLE} --verbose --testdir $PWD --suffix ${{ matrix.os }}_${{ matrix.mpi }} --mpi=auto
 
     - name: 'Tar output files'
       id: tar-package
@@ -201,35 +201,33 @@ jobs:
            for tgz in downloaded_artifacts/*/*.tgz; do
              work=$(mktemp -d)
              tar xzf "$tgz" -C "$work"
-             labeldir=$(ls -d "$work"/run_test-suite/*/)
-             mv "$labeldir" mcxtrace-nightly/
-
-             # Linux (ubuntu-latest) is the reference platform; the label
-             # name itself embeds a version string and timestamp we can't
-             # predict, so identify it via the source artifact/tarball name
-             # instead of hardcoding it.
-             if [[ "$tgz" == *"ubuntu-latest"* ]]; then
+             artifact_name=$(basename "$(dirname "$tgz")")
+
+             for labeldir in "$work"/run_test-suite/*/; do
+               if [[ "$artifact_name" == *"ubuntu-latest"* ]]; then
                REFLABEL=$(basename "$labeldir")
              fi
+               mv $labeldir mcxtrace-nightly/
+               done
+             done
              rm -rf "$work"
-           done
 
            if [ -z "$REFLABEL" ]; then
-             echo "ERROR: could not identify the Linux/reference column (ubuntu-latest artifact missing?)"
-             exit 1
-           fi
-
+             echo "WARNING: could not identify the ubuntu-latest/conda reference column"
+           else
            echo "REFLABEL=$REFLABEL" >> "$GITHUB_ENV"
            echo "Reference column: $REFLABEL"
-           ls mcxtrace-nightly
+           fi
 
     - name: 'Run mxviewtest across all platform columns'
       id: viewtest
       run: |
-           set -e
-           set -u
-           set -x
-           cd "$PWD/mcxtrace-nightly" && mxviewtest --reflabel "$REFLABEL" --nobrowse
+           cd "$PWD/mcxtrace-nightly"
+           if [ -z "$REFLABEL" ]; then
+             mxviewtest --reflabel "$REFLABEL" --nobrowse
+           else
+             mxviewtest --reflabel --nobrowse
+           fi
 
     - name: 'Tar mcxtrace-nightly output (all platform folders + comparison table)'
       id: tar-package
diff --git a/mcstas-comps/samples/PowderN.comp b/mcstas-comps/samples/PowderN.comp
index 36f6baf58..81809bea1 100644
--- a/mcstas-comps/samples/PowderN.comp
+++ b/mcstas-comps/samples/PowderN.comp
@@ -745,7 +745,10 @@ SHARE
     /* check if a line_info element has been recorded already - not on OpenACC */
     #ifndef OPENACC
     if (v >= line_info->v_min && v <= line_info->v_max && line_info->neutron_passed >= CHAR_BUF_LENGTH) {
-      line = (int)floor (v - line_info->v_min) * CHAR_BUF_LENGTH / (line_info->v_max - line_info->v_min);
+      double frac = (v - line_info->v_min) / (line_info->v_max - line_info->v_min);
+      line = (int)floor(frac * CHAR_BUF_LENGTH);
+      if (line < 0) line = 0;
+      if (line >= CHAR_BUF_LENGTH) line = CHAR_BUF_LENGTH - 1;
       Nq = line_info->xs_Nq[line];
       *sum = line_info->xs_sum[line];
       if (!Nq && *sum == 0) {
@@ -1172,10 +1175,11 @@ TRACE
       if (neutrontype == 3) { /* Make coherent scattering event */
         if (line_info.count > 0) {
           /* choose line */
-          if (Nq > 1)
+          if (Nq > 1) {
             line = floor (Nq * rand01 ()); /* Select between Nq powder lines */
-          else
-            line = 0;
+            if (line >= Nq) line = (int)Nq - 1; /* guard rand01()==1.0 edge case */
+           } else
+               line = 0;
           if (line_info.w_v[line])
             arg = line_info.q_v[line] * (1 + line_info.w_v[line] * randnorm ()) / (2.0 * v);
           else
diff --git a/mcxtrace-comps/samples/PowderN.comp b/mcxtrace-comps/samples/PowderN.comp
index 554381372..6599e9548 100644
--- a/mcxtrace-comps/samples/PowderN.comp
+++ b/mcxtrace-comps/samples/PowderN.comp
@@ -596,7 +596,10 @@ SHARE
     /* check if a line_info element has been recorded already - not on OpenACC */
     #ifndef OPENACC
     if (k >= line_info->k_min && k <= line_info->k_max && line_info->photon_passed >= CHAR_BUF_LENGTH) {
-      line = (int)floor (k - line_info->k_min) * CHAR_BUF_LENGTH / (line_info->k_max - line_info->k_min);
+      double frac = (k - line_info->k_min) / (line_info->k_max - line_info->k_min);
+      line = (int)floor(frac * CHAR_BUF_LENGTH);
+      if (line < 0) line = 0;
+      if (line >= CHAR_BUF_LENGTH) line = CHAR_BUF_LENGTH - 1;
       Nq = line_info->xs_Nq[line];
       *sum = line_info->xs_sum[line];
       if (!Nq && *sum == 0) {
@@ -1070,9 +1073,10 @@ TRACE
       if (photontype == 3) { /* Make coherent scattering event */
         if (line_info.count > 0) {
           /* choose line */
-          if (Nq > 1)
+          if (Nq > 1) {
             line = floor (Nq * rand01 ()); /* Select between Nq powder lines */
-          else
+            if (line >= Nq) line = (int)Nq - 1; /* guard rand01()==1.0 edge case */
+           } else
             line = 0;
           if (line_info.w[line])
             arg = line_info.q[line] * (1 + line_info.w[line] * randnorm ()) / (2.0 * k);