diff --git a/tests/ext/background-sender/agent_headers_container_id_fargate.phpt b/tests/ext/background-sender/agent_headers_container_id_fargate.phpt
index fa4fccffb7e..9a6dae7a944 100644
--- a/tests/ext/background-sender/agent_headers_container_id_fargate.phpt
+++ b/tests/ext/background-sender/agent_headers_container_id_fargate.phpt
@@ -9,7 +9,7 @@ DD_TRACE_BGS_ENABLED=1
 DD_AGENT_HOST=request-replayer
 DD_TRACE_AGENT_PORT=80
 DD_TRACE_AGENT_FLUSH_AFTER_N_REQUESTS=1
-DD_TRACE_AGENT_FLUSH_INTERVAL=333
+DD_TRACE_AGENT_FLUSH_INTERVAL=666
 DD_TRACE_GENERATE_ROOT_SPAN=0
 DD_INSTRUMENTATION_TELEMETRY_ENABLED=0
 --INI--
diff --git a/tests/ext/request-replayer/client_side_stats.phpt b/tests/ext/request-replayer/client_side_stats.phpt
index 3e20b8a6cc4..ee448cbeabc 100644
--- a/tests/ext/request-replayer/client_side_stats.phpt
+++ b/tests/ext/request-replayer/client_side_stats.phpt
@@ -27,6 +27,7 @@ DD_TRACE_GENERATE_ROOT_SPAN=0
 DD_INSTRUMENTATION_TELEMETRY_ENABLED=0
 DD_TRACE_SIDECAR_TRACE_SENDER=1
 DD_TRACE_STATS_COMPUTATION_ENABLED=1
+DD_TRACE_LOG_LEVEL=off
 --INI--
 datadog.env=test-env
 datadog.version=1.2.3-basic
diff --git a/tests/ext/shm_data_internal_fns.phpt b/tests/ext/shm_data_internal_fns.phpt
index cd85e14ba44..a1b8b3ff3ee 100644
--- a/tests/ext/shm_data_internal_fns.phpt
+++ b/tests/ext/shm_data_internal_fns.phpt
@@ -34,6 +34,7 @@ DD_REMOTE_CONFIG_POLL_INTERVAL_SECONDS=0.1
 DD_TRACE_SIDECAR_TRACE_SENDER=1
 DD_DYNAMIC_INSTRUMENTATION_ENABLED=1
 DD_TRACE_IGNORE_AGENT_SAMPLING_RATES=0
+DD_TRACE_LOG_LEVEL=off
 --INI--
 datadog.service=shm_data_test
 datadog.env=test
@@ -64,9 +65,16 @@ $rr->setResponse(['rate_by_service' => [
 dd_trace_internal_fn('synchronous_flush'); // ensure sidecar sends immediately
 $rr->waitForDataAndReplay();
 
-for ($i = 0; $i < 50; $i++) {
+// Under concurrent run-tests load the best-effort synchronous_flush above can
+// time out, delaying delivery of the trace that makes the replayer return the
+// sampling rates. Re-trigger the flush periodically and poll generously so the
+// agent sampling config eventually propagates into SHM.
+for ($i = 0; $i < 100; $i++) {
     $sampling = dd_trace_internal_fn('get_agent_sampling_config');
     if (!empty($sampling)) { break; }
+    if ($i % 10 === 9) {
+        dd_trace_internal_fn('synchronous_flush');
+    }
     usleep(100000);
 }
 var_dump(is_array($sampling));