diff --git a/GPU/GPUTracking/Base/GPUProcessor.h b/GPU/GPUTracking/Base/GPUProcessor.h
index 337ecfc61f79d..bbc156be88e06 100644
--- a/GPU/GPUTracking/Base/GPUProcessor.h
+++ b/GPU/GPUTracking/Base/GPUProcessor.h
@@ -51,6 +51,7 @@ class GPUProcessor
   GPUd() GPUconstantref() const GPUConstantMem* GetConstantMem() const; // Body in GPUConstantMem.h to avoid circular headers
   GPUd() GPUconstantref() const GPUParam& Param() const;                // ...
   GPUd() void raiseError(uint32_t code, uint32_t param1 = 0, uint32_t param2 = 0, uint32_t param3 = 0) const;
+  GPUd() bool IsDeviceProcessor() const { return mGPUProcessorType == PROCESSOR_TYPE_DEVICE; }
   const GPUReconstruction& GetRec() const { return *mRec; }
 
 #ifndef __OPENCL__
diff --git a/GPU/GPUTracking/Merger/GPUTPCGMMerger.cxx b/GPU/GPUTracking/Merger/GPUTPCGMMerger.cxx
index e8c98bf4b4a45..e8f7c761c1dac 100644
--- a/GPU/GPUTracking/Merger/GPUTPCGMMerger.cxx
+++ b/GPU/GPUTracking/Merger/GPUTPCGMMerger.cxx
@@ -640,6 +640,7 @@ GPUd() void GPUTPCGMMerger::UnpackSectorGlobal(int32_t nBlocks, int32_t nThreads
     SetTrackClusterT(track, iSector, sectorTr);
     track.Set(this, sectorTr, alpha, iSector);
     track.SetGlobalSectorTrackCov();
+    track.SetX2(0.f);
     track.SetPrevNeighbour(-1);
     track.SetNextNeighbour(-1);
     track.SetNextSegmentNeighbour(-1);
diff --git a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
index e71bfea61112c..86fe293a99bfe 100644
--- a/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
+++ b/GPU/GPUTracking/TPCClusterFinder/GPUTPCCFDecodeZS.cxx
@@ -48,7 +48,8 @@ GPUdii() void GPUTPCCFDecodeZS::decode(GPUTPCClusterFinder& clusterer, GPUShared
 #ifdef GPUCA_GPUCODE
   const uint32_t endpoint = clusterer.mPzsOffsets[iBlock].endpoint;
 #else
-  const uint32_t endpoint = iBlock;
+  const bool deviceLayout = clusterer.IsDeviceProcessor(); // Host-compiled kernel running with threading as on a device
+  const uint32_t endpoint = deviceLayout ? clusterer.mPzsOffsets[iBlock].endpoint : iBlock;
 #endif
   const GPUTrackingInOutZS::GPUTrackingInOutZSSector& zs = clusterer.GetConstantMem()->ioPtrs.tpcZS->sector[sector];
   if (zs.count[endpoint] == 0) {
@@ -74,9 +75,11 @@ GPUdii() void GPUTPCCFDecodeZS::decode(GPUTPCClusterFinder& clusterer, GPUShared
   {
     {
 #else
-  for (uint32_t i = clusterer.mMinMaxCN[endpoint].zsPtrFirst; i < clusterer.mMinMaxCN[endpoint].zsPtrLast; i++) {
-    const uint32_t minJ = (i == clusterer.mMinMaxCN[endpoint].zsPtrFirst) ? clusterer.mMinMaxCN[endpoint].zsPageFirst : 0;
-    const uint32_t maxJ = (i + 1 == clusterer.mMinMaxCN[endpoint].zsPtrLast) ? clusterer.mMinMaxCN[endpoint].zsPageLast : zs.nZSPtr[endpoint][i];
+  const uint32_t iFirst = deviceLayout ? 0 : clusterer.mMinMaxCN[endpoint].zsPtrFirst;
+  const uint32_t iLast = deviceLayout ? 1 : clusterer.mMinMaxCN[endpoint].zsPtrLast;
+  for (uint32_t i = iFirst; i < iLast; i++) {
+    const uint32_t minJ = deviceLayout ? clusterer.mPzsOffsets[iBlock].num : ((i == iFirst) ? clusterer.mMinMaxCN[endpoint].zsPageFirst : 0);
+    const uint32_t maxJ = deviceLayout ? (minJ + 1) : ((i + 1 == iLast) ? clusterer.mMinMaxCN[endpoint].zsPageLast : zs.nZSPtr[endpoint][i]);
     for (uint32_t j = minJ; j < maxJ; j++) {
 #endif
       const uint32_t* pageSrc = (const uint32_t*)(((const uint8_t*)zs.zsPtr[endpoint][i]) + j * TPCZSHDR::TPC_ZS_PAGE_SIZE);
@@ -370,7 +373,8 @@ GPUd() void GPUTPCCFDecodeZSLinkBase::Decode(int32_t nBlocks, int32_t nThreads,
 #ifdef GPUCA_GPUCODE
   const uint32_t endpoint = clusterer.mPzsOffsets[iBlock].endpoint;
 #else // CPU
-  const uint32_t endpoint = iBlock;
+  const bool deviceLayout = clusterer.IsDeviceProcessor(); // Host-compiled kernel running as device kernel (CPUDevice backend): GPU work distribution, one block per page
+  const uint32_t endpoint = deviceLayout ? clusterer.mPzsOffsets[iBlock].endpoint : iBlock;
 #endif
 
   const GPUTrackingInOutZS::GPUTrackingInOutZSSector& zs = clusterer.GetConstantMem()->ioPtrs.tpcZS->sector[sector];
@@ -386,9 +390,11 @@ GPUd() void GPUTPCCFDecodeZSLinkBase::Decode(int32_t nBlocks, int32_t nThreads,
   {
     {
 #else // CPU
-  for (uint32_t i = clusterer.mMinMaxCN[endpoint].zsPtrFirst; i < clusterer.mMinMaxCN[endpoint].zsPtrLast; i++) {
-    const uint32_t minJ = (i == clusterer.mMinMaxCN[endpoint].zsPtrFirst) ? clusterer.mMinMaxCN[endpoint].zsPageFirst : 0;
-    const uint32_t maxJ = (i + 1 == clusterer.mMinMaxCN[endpoint].zsPtrLast) ? clusterer.mMinMaxCN[endpoint].zsPageLast : zs.nZSPtr[endpoint][i];
+  const uint32_t iFirst = deviceLayout ? 0 : clusterer.mMinMaxCN[endpoint].zsPtrFirst;
+  const uint32_t iLast = deviceLayout ? 1 : clusterer.mMinMaxCN[endpoint].zsPtrLast;
+  for (uint32_t i = iFirst; i < iLast; i++) {
+    const uint32_t minJ = deviceLayout ? clusterer.mPzsOffsets[iBlock].num : ((i == iFirst) ? clusterer.mMinMaxCN[endpoint].zsPageFirst : 0);
+    const uint32_t maxJ = deviceLayout ? (minJ + 1) : ((i + 1 == iLast) ? clusterer.mMinMaxCN[endpoint].zsPageLast : zs.nZSPtr[endpoint][i]);
     for (uint32_t j = minJ; j < maxJ; j++) {
 #endif
       const uint32_t* pageSrc = (const uint32_t*)(((const uint8_t*)zs.zsPtr[endpoint][i]) + j * TPCZSHDR::TPC_ZS_PAGE_SIZE);
diff --git a/GPU/GPUTracking/TPCClusterFinder/GPUTPCClusterFinder.cxx b/GPU/GPUTracking/TPCClusterFinder/GPUTPCClusterFinder.cxx
index 06709ef2d4a7e..c0c869d0dcc9b 100644
--- a/GPU/GPUTracking/TPCClusterFinder/GPUTPCClusterFinder.cxx
+++ b/GPU/GPUTracking/TPCClusterFinder/GPUTPCClusterFinder.cxx
@@ -161,6 +161,9 @@ uint32_t GPUTPCClusterFinder::getNSteps(size_t items) const
   }
   uint32_t c = 1;
   const size_t scanWorkgroupSize = mRec->getGPUParameters(mRec->GetRecoStepsGPU() & gpudatatypes::RecoStep::TPCClusterFinding).par_CF_SCAN_WORKGROUP_SIZE;
+  if (scanWorkgroupSize <= 1) {
+    return 1;
+  }
   size_t capacity = scanWorkgroupSize;
   while (items > capacity) {
     capacity *= scanWorkgroupSize;