I have recently updated and rebuilt my MM installation.
I can browse to my MM via a remote web browser and things display fine, however on the HDMI output of the PI itself I just have a black screen.

In the logs I see,

[1502:0115/164948.881957:ERROR:viz_main_impl.cc(186)] Exiting GPU process due to errors during initialization
[1538:0115/164949.052412:ERROR:gpu_memory_buffer_support_x11.cc(44)] dri3 extension not supported.
[1507:0115/164949.107262:ERROR:command_buffer_proxy_impl.cc(128)] ContextResult::kTransientFailure: Failed to send GpuControl.CreateCommandBuffer.

I wonder if anyone might be able to point me in the right direction.