Do you have a pic of the part after printing? Did it need supports to print? If so, the Markforged website says to leave them on while sintering, "When the binder melts away, there is a period during which the part is effectively a sandcastle. The supports are critical to keeping overhang features from falling over during this step of the sintering process."
https://markforged.com/resources/blog/metal-3d-printing


When I sinter an oddly-shaped piece of silver clay, I support it on a bed of vermiculite. After sintering, the piece looks solid, but is actually porous. This makes it brittle, so you need to treat it more gently than a solid piece. I imagine that the Markforged stainless steel would also be somewhat porous after sintering.