Problem is that the RenderEngines will change the RenderData cfra when
rendering (when time remapping is used -- at least workbench/eevee/
gpencil do a combination of BKE_scene_frame_get() plus
RE_GetCameraWindow() which alters the RenderData cfra).
Later on in the pipeline, the Compositor will use this RenderData cfra
to determine the output file name for the FileOutput node. (In contrast
to this, the 'regular' Output will use the Scene's RenderData -- not the
Render's -- cfra [which hasnt been altered])
It is not entirely clear why RE_GetCameraWindow was setting the cfra on the Render, but it appears to be legacy OGL rendering related and is not needed anymore.
Removing this will keep the cfra as needed for the Compositor FileOutput node.