Cycles uses multiple threads to send commands to the GPU. The current
command buffer structure assumed that all commands from the same context
were send via the same thread. This wasn't the case and could lead to
recording commands to command buffers that are still pending (preparing
commands to send to GPU).
This is fixed by creating a command buffer each time a render graph
submits its work.
Detected when researching #128608
Pull Request: https://projects.blender.org/blender/blender/pulls/128978
fb862d082a