difference in size between saved plot and fig

I do not understand why plots differ in terms of size and how they look when I try to save them or returnfig.

I generate plots of figsize (9,4) when I save them they look great, with a tight layout, no margins and axes excellent! But I need these plots again so it would be better to use a buffer instead. However, when I use the buffer resulting plot has a different size and added margins on one side.

The saved plot has size (365, 801, 1) while plot from the buffer (400, 900, 1).

I appreciate any suggestions how to use buffer but without adding margins.
Thank you

Reproduce el gráfico usando figsize (9,4), guardándolo primero y recuperándolo después mediante un búfer con returnfig. Compara las dimensiones y los márgenes resultantes, incluidos los tamaños indicados (365, 801, 1) y (400, 900, 1). Se considera terminado cuando el resultado del búfer coincide con el gráfico guardado sin los márgenes añadidos.