Seems to happen only on WPE Debug bot... And I don't remember seeing this before the SDK update to 23.08.

Thread 1 (Thread 0x7f4d329d0180 (LWP 701906)):
#0  g_logv (log_domain=0x0, log_level=G_LOG_LEVEL_CRITICAL, format=<optimized out>, args=args@entry=0x7ffc7d8cd650) at ../glib/gmessages.c:1422
#1  0x00007f4d398b57a3 in g_log (log_domain=log_domain@entry=0x0, log_level=log_level@entry=G_LOG_LEVEL_CRITICAL, format=format@entry=0x7f4d3990df92 "%s: assertion '%s' failed") at ../glib/gmessages.c:1460
#2  0x00007f4d398b861d in g_return_if_fail_warning (log_domain=log_domain@entry=0x0, pretty_function=pretty_function@entry=0x7f4c98365b00 <__func__.22> "webrtc_data_channel_send_string", expression=expression@entry=0x7f4c983609e1 "channel->opened") at ../glib/gmessages.c:2930
#3  0x00007f4c98355edd in webrtc_data_channel_send_string (base_channel=0x55ad3cb40170, str=0x55ad3b30ad00 "one", error=0x0) at ../ext/webrtc/webrtcdatachannel.c:926
#4  0x00007f4d35a5fdab in g_cclosure_marshal_VOID__STRINGv (closure=0x55ad3ce874a0, return_value=<optimized out>, instance=<optimized out>, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, param_types=0x55ad3b2242d0) at ../gobject/gmarshal.c:1462
#5  0x00007f4d35a81a83 in _g_closure_invoke_va (param_types=0x55ad3b2242d0, n_params=<optimized out>, args=0x7ffc7d8cd980, instance=0x55ad3cb40170, return_value=<optimized out>, closure=<optimized out>) at ../gobject/gclosure.c:895
#6  g_signal_emit_valist (instance=instance@entry=0x55ad3cb40170, signal_id=signal_id@entry=113, detail=<optimized out>, var_args=var_args@entry=0x7ffc7d8cd980) at ../gobject/gsignal.c:3472
#7  0x00007f4d35a81e2a in g_signal_emit_by_name (instance=0x55ad3cb40170, detailed_signal=0x7f4d3a6af836 "send-string") at ../gobject/gsignal.c:3664
#8  0x00007f4d3e8d0655 in WebCore::GStreamerDataChannelHandler::sendStringData(WTF::CString const&) () at /app/webkit/WebKitBuild/WPE/Release/lib/libWPEWebKit-2.0.so.1
#9  0x00007f4d3e8a6730 in WTF::Detail::CallableWrapper<WebCore::RTCDataChannel::createMessageQueue(WebCore::ScriptExecutionContext&, WebCore::RTCDataChannel&)::{lambda(auto:1&)#1}, void, WTF::CString const&>::call(WTF::CString const&) () at /app/webkit/WebKitBuild/WPE/Release/lib/libWPEWebKit-2.0.so.1
#10 0x00007f4d3e8a3af8 in WebCore::RTCDataChannel::send(WTF::String const&) () at /app/webkit/WebKitBuild/WPE/Release/lib/libWPEWebKit-2.0.so.1
#11 0x00007f4d3e1d26c6 in WebCore::jsRTCDataChannelPrototypeFunction_send(JSC::JSGlobalObject*, JSC::CallFrame*) () at /app/webkit/WebKitBuild/WPE/Release/lib/libWPEWebKit-2.0.so.1
#12 0x00007f4ce81d41b8 in  ()
#13 0x00007ffc7d8cdca0 in  ()
#14 0x00007f4d4036c445 in op_call_ignore_result_return_location () at /app/webkit/WebKitBuild/WPE/Release/lib/libWPEWebKit-2.0.so.1
#15 0x0000000000000000 in  ()

STDERR: ** (WPEWebProcess:701906): CRITICAL **: 06:42:38.103: webrtc_data_channel_send_string: assertion 'channel->opened' failed