diff --git a/.github/workflows/alpine/Dockerfile.ci b/.github/workflows/alpine/Dockerfile.ci
index 291a18345ba0..1d77900b772b 100644
--- a/.github/workflows/alpine/Dockerfile.ci
+++ b/.github/workflows/alpine/Dockerfile.ci
@@ -57,6 +57,7 @@ RUN apk add \
     py3-pyarrow-pyc \
     py3-numpy \
     py3-numpy-dev \
+    py3-numpy-tests \
     py3-pip \
     py3-setuptools \
     python3-dev \
diff --git a/.github/workflows/alpine_32bit/Dockerfile.ci b/.github/workflows/alpine_32bit/Dockerfile.ci
index 935527a4a707..b16711eedee8 100644
--- a/.github/workflows/alpine_32bit/Dockerfile.ci
+++ b/.github/workflows/alpine_32bit/Dockerfile.ci
@@ -58,6 +58,7 @@ RUN apk add \
     py3-pyarrow-pyc \
     py3-numpy \
     py3-numpy-dev \
+    py3-numpy-tests \
     py3-pip \
     py3-setuptools \
     python3-dev \
diff --git a/autotest/ogr/ogr_dxf.py b/autotest/ogr/ogr_dxf.py
index b07e71d3d5c3..cc61c92f8d9c 100644
--- a/autotest/ogr/ogr_dxf.py
+++ b/autotest/ogr/ogr_dxf.py
@@ -3881,7 +3881,7 @@ def test_ogr_dxf_53():
 # Test frozen and off layers
 
 
-def test_ogr_dxf_54():
+def test_ogr_dxf_54(tmp_vsimem):
 
     with gdal.config_option("DXF_MERGE_BLOCK_GEOMETRIES", "FALSE"):
         ds = ogr.Open("data/dxf/frozen-off.dxf")
@@ -3897,7 +3897,36 @@ def test_ogr_dxf_54():
         )
         if isFeatureVisible == (h == "h"):
             f.DumpReadable()
-            pytest.fail("Wrong visibility on feature %d" % number)
+            pytest.fail(
+                "Wrong visibility on feature %d (testing with layer 0 thawed)" % number
+            )
+
+    # Rewrite the test file, this time with layer 0 set as frozen
+    with open("data/dxf/frozen-off.dxf", "r") as file:
+        gdal.FileFromMemBuffer(
+            tmp_vsimem / "frozen-off-with-layer0-frozen.dxf",
+            file.read().replace(
+                "0\nLAYER\n  2\n0\n 70\n     0", "0\nLAYER\n  2\n0\n 70\n     1"
+            ),
+        )
+
+    with gdal.config_option("DXF_MERGE_BLOCK_GEOMETRIES", "FALSE"):
+        ds = ogr.Open(
+            tmp_vsimem / "frozen-off-with-layer0-frozen.dxf",
+        )
+    lyr = ds.GetLayer(0)
+
+    # Repeat test - outcome should be the same
+    for number, h in enumerate(featureVisibility):
+        f = lyr.GetNextFeature()
+        isFeatureVisible = (
+            "#000000)" in f.GetStyleString() or "#ff0000)" in f.GetStyleString()
+        )
+        if isFeatureVisible == (h == "h"):
+            f.DumpReadable()
+            pytest.fail(
+                "Wrong visibility on feature %d (testing with layer 0 frozen)" % number
+            )
 
 
 ###############################################################################
diff --git a/ogr/ogrct.cpp b/ogr/ogrct.cpp
index ae93f7163579..f04c993677c2 100644
--- a/ogr/ogrct.cpp
+++ b/ogr/ogrct.cpp
@@ -21,7 +21,6 @@
 #include <limits>
 #include <list>
 #include <mutex>
-#include <thread>
 
 #include "cpl_conv.h"
 #include "cpl_error.h"
@@ -750,9 +749,6 @@ class OGRProjCT : public OGRCoordinateTransformation
 
     double dfThreshold = 0.0;
 
-    PJ_CONTEXT *m_psLastContext = nullptr;
-    std::thread::id m_nLastContextThreadId{};
-
     PjPtr m_pj{};
     bool m_bReversePj = false;
 
@@ -1265,10 +1261,9 @@ OGRProjCT::OGRProjCT(const OGRProjCT &other)
       m_osTargetSRS(other.m_osTargetSRS),
       bWebMercatorToWGS84LongLat(other.bWebMercatorToWGS84LongLat),
       nErrorCount(other.nErrorCount), dfThreshold(other.dfThreshold),
-      m_psLastContext(nullptr),
-      m_nLastContextThreadId(std::this_thread::get_id()), m_pj(other.m_pj),
-      m_bReversePj(other.m_bReversePj), m_bEmitErrors(other.m_bEmitErrors),
-      bNoTransform(other.bNoTransform), m_eStrategy(other.m_eStrategy),
+      m_pj(other.m_pj), m_bReversePj(other.m_bReversePj),
+      m_bEmitErrors(other.m_bEmitErrors), bNoTransform(other.bNoTransform),
+      m_eStrategy(other.m_eStrategy),
       m_oTransformations(other.m_oTransformations),
       m_iCurTransformation(other.m_iCurTransformation),
       m_options(other.m_options)
@@ -2520,14 +2515,7 @@ int OGRProjCT::TransformWithErrorCodes(size_t nCount, double *x, double *y,
     /*      Select dynamically the best transformation for the data, if     */
     /*      needed.                                                         */
     /* -------------------------------------------------------------------- */
-    PJ_CONTEXT *ctx = m_psLastContext;
-    const auto nThisThreadId = std::this_thread::get_id();
-    if (!ctx || nThisThreadId != m_nLastContextThreadId)
-    {
-        m_nLastContextThreadId = nThisThreadId;
-        m_psLastContext = OSRGetProjTLSContext();
-        ctx = m_psLastContext;
-    }
+    auto ctx = OSRGetProjTLSContext();
 
     PJ *pj = m_pj;
     if (!bTransformDone && !pj)
diff --git a/ogr/ogrsf_frmts/dxf/ogrdxf_feature.cpp b/ogr/ogrsf_frmts/dxf/ogrdxf_feature.cpp
index 8bb92b3aab50..36e395127f4e 100644
--- a/ogr/ogrsf_frmts/dxf/ogrdxf_feature.cpp
+++ b/ogr/ogrsf_frmts/dxf/ogrdxf_feature.cpp
@@ -146,9 +146,9 @@ OGRDXFFeature::GetColor(OGRDXFDataSource *const poDS,
         (poBlockFeature &&
          poBlockFeature->oStyleProperties.count("Hidden") > 0))
     {
-        // Hidden objects should never be shown no matter what happens,
-        // so they can be treated as if they are on a frozen layer
-        iHidden = 2;
+        // Hidden objects should never be shown no matter what happens
+        iHidden = 1;
+        oStyleProperties["Hidden"] = "1";
     }
     else
     {
@@ -166,13 +166,13 @@ OGRDXFFeature::GetColor(OGRDXFDataSource *const poDS,
             if (pszBlockHidden && atoi(pszBlockHidden) == 2)
                 iHidden = 2;
         }
-    }
 
-    // If this feature is on a frozen layer, make the object totally
-    // hidden so it won't reappear if we regenerate the style string again
-    // during block insertion
-    if (iHidden == 2)
-        oStyleProperties["Hidden"] = "1";
+        // If this feature is on a frozen layer (other than layer 0), make the
+        // object totally hidden so it won't reappear if we regenerate the style
+        // string again during block insertion
+        if (iHidden == 2 && !EQUAL(GetFieldAsString("Layer"), "0"))
+            oStyleProperties["Hidden"] = "1";
+    }
 
     // Helpful constants
     const int C_BYLAYER = 256;