On this point, I’m not so sure.
The suttas show that Samma Sambuddhas are exceptionally rare time wise, as 99% of Buddhas are pacceka Buddhas, it’s extremely rare for a Buddha to become a Samma Sambuddha.
Also, if you look at the list of Gotamas past life, they’re all in the indus valley region. So it seems like all Buddhas are from the Indus Valley region. So if someone is constantly reborn outside of that region, there’s even a less chance of the already extremely rare chance to meet a Samma Sambuddha.
The Buddha uses the simile of a blind turtle putting its head through a hole in a log as a metaphor to illustrate how exceptionally rare it is to be human and meet a samma sambuddha.
Monks, suppose that this great earth were totally covered with water, and a man were to toss a yoke with a single hole there. A wind from the east would push it west, a wind from the west would push it east. A wind from the north would push it south, a wind from the south would push it north. And suppose a blind sea-turtle were there. It would come to the surface once every one hundred years. Now what do you think: would that blind sea-turtle, coming to the surface once every one hundred years, stick his neck into the yoke with a single hole?"
“It would be a sheer coincidence, lord, that the blind sea-turtle, coming to the surface once every one hundred years, would stick his neck into the yoke with a single hole.”
"It’s likewise a sheer coincidence that one obtains the human state. It’s likewise a sheer coincidence that a Tathagata, worthy & rightly self-awakened, arises in the world. It’s likewise a sheer coincidence that a doctrine & discipline expounded by a Tathagata appears in the world. Now, this human state has been obtained. A Tathagata, worthy & rightly self-awakened, has arisen in the world. A doctrine & discipline expounded by a Tathagata appears in the world.
“Therefore your duty is the contemplation, ‘This is stress… This is the origination of stress… This is the cessation of stress.’ Your duty is the contemplation, ‘This is the path of practice leading to the cessation of stress.’”
So for someone to ordain under a samma Sambuddha and not become an ariya, or at least go to hell and become a buddha later if their karma-vipaka is really bad, I think is probably zero. I don’t think a Samma Sambuddha would even allow monks under him to not become an ariya, I don’t think it’s even possible technically, as that would imply the weakness of a Samma Sambuddha