Sources involved in the deal with the stroller co., Momiie, tell us ... it's pulled the plug on its collab with Chyna in wake of her stroller-swinging skirmish Sunday at Six Flags.

We're told the incident was not the sole reason for Momiie's decision. Honchos had already grown uneasy with Chyna's behavioral issues -- not to mention a leaked sex tape -- and the impact it might have on their brand. The fight video was definitely the final nail in the coffin.

A rep for Momiie adds Chyna's latest actions made it impossible to move forward with their business relationship, telling us ... "[We] cannot excuse that sort of reaction and behavior particularly in a family resort around children.”

We broke the story ... BC signed up to be a brand ambassador for the new baby strollers, with the goal of launching her own line with Momiie if all went well. It didn't.

Instead, Chyna might be in store for a legal war with Rob Kardashian, who's livid she put 1-year-old Dream in harm's way ... though Chyna claims she was actually defending their daughter.