mediaplayerexample example fails with 6.8.0 Beta4 and Rri4

You can reproduce the issue by downloading Beta4 SDK. Importing mediaplayer - example. Compile-deploy-run in Raspberry Pi 4 (with Beta4 running).

-> No video is shown. Qt_LogoMergeEffect.mp4 video should be playing automatically.

Output with GST_DEBUG=3

0:00:11.597952759   928   0x556faf8560 WARN                 basesrc gstbasesrc.c:3693:gst_base_src_start_complete:<source> pad not activated yet
0:00:11.598537582   928   0x556faf8560 WARN                 basesrc gstbasesrc.c:3693:gst_base_src_start_complete:<source> pad not activated yet
0:00:11.618274130   928   0x7f30000db0 WARN                 qtdemux qtdemux_types.c:266:qtdemux_type_get: unknown QuickTime node type .TIM
0:00:11.618335536   928   0x7f30000db0 WARN                 qtdemux qtdemux_types.c:266:qtdemux_type_get: unknown QuickTime node type .TSC
0:00:11.618357073   928   0x7f30000db0 WARN                 qtdemux qtdemux_types.c:266:qtdemux_type_get: unknown QuickTime node type .TSZ
0:00:11.618469719   928   0x7f30000db0 WARN                 qtdemux qtdemux.c:3248:qtdemux_parse_trex:<qtdemux0> failed to find fragment defaults for stream 1
0:00:11.654253309   928   0x7f30000ff0 WARN                    v4l2 gstv4l2object.c:3278:gst_v4l2_object_reset_compose_region:<v4l2h264dec0:sink> Failed to get default compose rectangle with VIDIOC_G_SELECTION: Invalid argument
0:00:11.665060002   928   0x7f30001230 WARN                    v4l2 gstv4l2object.c:2305:gst_v4l2_object_get_streamparm:<v4l2h264dec0:src> VIDIOC_G_PARM failed
QGstElement::state detected an asynchronous state change. Return value not reliable
0:00:11.670029578   928   0x7f30001230 WARN                GST_PADS gstpad.c:4387:gst_pad_peer_query:<v4l2h264dec0:src> could not send sticky events

With GST_DEBUG=5 the issue is not reproducable. Video starts playing. I't really laggy though.