diff --git a/.github/workflows/release-test.yml b/.github/workflows/release-test.yml
index ce3152f5e6..48651d16c7 100644
--- a/.github/workflows/release-test.yml
+++ b/.github/workflows/release-test.yml
@@ -123,6 +123,7 @@ jobs:
         sudo apt-get install lib32asan6
     - name: Run release tests
       timeout-minutes: 350
+      id: tests
       run: |
         RIOTBASE="$GITHUB_WORKSPACE/RIOT"
         TOX_ARGS=""
@@ -173,6 +174,27 @@ jobs:
         mkdir test-reports/
         junit2html ${REPORT_XML} ${REPORT_NAME}.html
         cp ${REPORT_XML} ${REPORT_NAME}.xml
+    - name: Generate result message
+      if: always()
+      id: generate_results
+      run: |
+        if [ "${{ steps.tests.conclusion }}" == "success" ]; then
+          nice_str=echo "✅ **PASSED**"
+        elif [ "${{ steps.tests.conclusion }}" == "failure" ]; then
+          nice_str="❌ **FAILED**"
+        fi
+        echo "nice_str=${nice_str}" >> ${GITHUB_OUTPUT}
+    - name: Report to Matrix channel
+      if: ${{ always() && steps.generate_results.outputs.nice_str != '' }}
+      uses: fadenb/matrix-chat-message@v0.0.6
+      with:
+        homeserver: matrix.org
+        token: ${{ secrets.RIOT_CI_MATRIX_TOKEN }}
+        channel: '!UXNJuMzHTSAnwntbbN:utwente.io'
+        message: |
+          ${{ steps.generate_results.outputs.nice_str}}: Release tests
+          [${{ matrix.pytest_mark }}, ${{ matrix.sudo }}] on "*${{ github.event_name }}*":
+          ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
     - uses: actions/upload-artifact@v2
       if: always()
       with:
diff --git a/boards/common/makefiles/stdio_cdc_acm.dep.mk b/boards/common/makefiles/stdio_cdc_acm.dep.mk
index cbd3047533..140bf7114a 100644
--- a/boards/common/makefiles/stdio_cdc_acm.dep.mk
+++ b/boards/common/makefiles/stdio_cdc_acm.dep.mk
@@ -8,4 +8,9 @@ ifeq (,$(filter-out stdio_cdc_acm,$(filter stdio_% slipdev_stdio,$(USEMODULE))))
     USEMODULE += stdio_cdc_acm
   endif
   FEATURES_REQUIRED += highlevel_stdio
+
+  # Enforce tests to wait a bit for the serial port after reset
+  TERM_DELAY ?= 2
+  TESTRUNNER_CONNECT_DELAY ?= $(TERM_DELAY)
+  $(call target-export-variables,test,TESTRUNNER_CONNECT_DELAY)
 endif
diff --git a/makefiles/utils/strings.mk b/makefiles/utils/strings.mk
index 66467c2988..cbc280fcf0 100644
--- a/makefiles/utils/strings.mk
+++ b/makefiles/utils/strings.mk
@@ -7,8 +7,8 @@ lowercase = $(subst A,a,$(subst B,b,$(subst C,c,$(subst D,d,$(subst E,e,$(subst
 uppercase = $(subst a,A,$(subst b,B,$(subst c,C,$(subst d,D,$(subst e,E,$(subst f,F,$(subst g,G,$(subst h,H,$(subst i,I,$(subst j,J,$(subst k,K,$(subst l,L,$(subst m,M,$(subst n,N,$(subst o,O,$(subst p,P,$(subst q,Q,$(subst r,R,$(subst s,S,$(subst t,T,$(subst u,U,$(subst v,V,$(subst w,W,$(subst x,X,$(subst y,Y,$(subst z,Z,$1))))))))))))))))))))))))))
 uppercase_and_underscore = $(call uppercase,$(subst -,_,$1))
 
-# Padds $2 number to $1 digits
-_pad_number = $(shell printf '%0$1d' $2)
+# Padds number $2 to $1 digits. If $2 is empty, zero will be printed instead.
+_pad_number = $(shell printf '%0$1d' $(if $2,$2,0))
 
 # Gets major, minor, patch from 'major.minor.patch', e.g.: 4.2.1 by index
 #   $1: index
diff --git a/tests/congure_abe/tests/01-run.py b/tests/congure_abe/tests/01-run.py
index 714ab79bf6..b098aa5c1d 100755
--- a/tests/congure_abe/tests/01-run.py
+++ b/tests/congure_abe/tests/01-run.py
@@ -8,6 +8,7 @@
 
 import logging
 import sys
+import time
 import unittest
 
 from riotctrl.ctrl import RIOTCtrl
@@ -15,6 +16,8 @@ from riotctrl.shell.json import RapidJSONShellInteractionParser, rapidjson
 
 from riotctrl_shell.congure_test import CongureTest
 
+from testrunner.spawn import MAKE_TERM_CONNECT_DELAY
+
 
 class TestCongUREBase(unittest.TestCase):
     # pylint: disable=too-many-public-methods
@@ -25,6 +28,7 @@ class TestCongUREBase(unittest.TestCase):
     def setUpClass(cls):
         cls.ctrl = RIOTCtrl()
         cls.ctrl.reset()
+        time.sleep(MAKE_TERM_CONNECT_DELAY)
         cls.ctrl.start_term()
         if cls.DEBUG:
             cls.ctrl.term.logfile = sys.stdout
diff --git a/tests/congure_quic/tests/01-run.py b/tests/congure_quic/tests/01-run.py
index 1b1165b06c..8d0ef8b936 100755
--- a/tests/congure_quic/tests/01-run.py
+++ b/tests/congure_quic/tests/01-run.py
@@ -8,6 +8,7 @@
 
 import logging
 import sys
+import time
 import unittest
 
 from riotctrl.ctrl import RIOTCtrl
@@ -15,6 +16,8 @@ from riotctrl.shell.json import RapidJSONShellInteractionParser, rapidjson
 
 from riotctrl_shell.congure_test import CongureTest
 
+from testrunner.spawn import MAKE_TERM_CONNECT_DELAY
+
 
 class TestCongUREBase(unittest.TestCase):
     DEBUG = False
@@ -25,6 +28,7 @@ class TestCongUREBase(unittest.TestCase):
     def setUpClass(cls):
         cls.ctrl = RIOTCtrl()
         cls.ctrl.reset()
+        time.sleep(MAKE_TERM_CONNECT_DELAY)
         cls.ctrl.start_term()
         if cls.DEBUG:
             cls.ctrl.term.logfile = sys.stdout
diff --git a/tests/congure_reno/tests/01-run.py b/tests/congure_reno/tests/01-run.py
index 0b08dd0880..993ff645fc 100755
--- a/tests/congure_reno/tests/01-run.py
+++ b/tests/congure_reno/tests/01-run.py
@@ -8,6 +8,7 @@
 
 import logging
 import sys
+import time
 import unittest
 
 from riotctrl.ctrl import RIOTCtrl
@@ -15,6 +16,8 @@ from riotctrl.shell.json import RapidJSONShellInteractionParser, rapidjson
 
 from riotctrl_shell.congure_test import CongureTest
 
+from testrunner.spawn import MAKE_TERM_CONNECT_DELAY
+
 
 class TestCongUREBase(unittest.TestCase):
     # pylint: disable=too-many-public-methods
@@ -25,6 +28,7 @@ class TestCongUREBase(unittest.TestCase):
     def setUpClass(cls):
         cls.ctrl = RIOTCtrl()
         cls.ctrl.reset()
+        time.sleep(MAKE_TERM_CONNECT_DELAY)
         cls.ctrl.start_term()
         if cls.DEBUG:
             cls.ctrl.term.logfile = sys.stdout
diff --git a/tests/congure_test/tests/01-run.py b/tests/congure_test/tests/01-run.py
index 677606cf2d..4db47e2d4e 100755
--- a/tests/congure_test/tests/01-run.py
+++ b/tests/congure_test/tests/01-run.py
@@ -9,6 +9,7 @@
 import logging
 import os
 import sys
+import time
 import unittest
 
 from riotctrl.ctrl import RIOTCtrl
@@ -17,6 +18,8 @@ from riotctrl.shell.json import RapidJSONShellInteractionParser, rapidjson
 
 from riotctrl_shell.congure_test import CongureTest
 
+from testrunner.spawn import MAKE_TERM_CONNECT_DELAY
+
 
 class TestCongUREBase(unittest.TestCase):
     DEBUG = False
@@ -25,6 +28,7 @@ class TestCongUREBase(unittest.TestCase):
     def setUpClass(cls):
         cls.ctrl = RIOTCtrl()
         cls.ctrl.reset()
+        time.sleep(MAKE_TERM_CONNECT_DELAY)
         cls.ctrl.start_term()
         if cls.DEBUG:
             cls.ctrl.term.logfile = sys.stdout