https://en.wikipedia.org/wiki/Unreliable_narrator
I think this basically covers Yhwach's foresight. Only the bad guys have confirmed that he has it at all, and of course they're all claiming it's perfect. But I just think Yhwach can't really predict Ichigo at all, and his predictions for him are just him being smart enough to predict Ichigo's behavior.
Basically, I trust Yhwach's foresight as much as I trust Aizen's invincibility. Ichigo's immune to both.
I bet he can't predict the influence of Hollows on events, so Ichigo embracing and controlling his Hollow side makes him a "blind spot" to Almighty. Like, if you imagine Yhwach as watching a bunch of video feeds of everything happening in the world, as soon as Ichigo switches on Hollow powers it's like the monitor labelled "Ichigo" turns to static, then it comes back on when Ichigo returns to "normal."
Yhwach can possibly see the "results" then, but he doesn't know what actually lead up to them since a Hollow was a major player, and he can misinterpret or be mislead by what he sees the future as.
Come to think of it, typing that out made me think that Ichigo will do to Yhwach what White did to his mother. Yhwach has "seen" the result of this battle as being him cutting down Ichigo, but maybe Ichigo lets himself be cut by Yhwach's blade or otherwise sacrifices himself to "infect" Yhwach, destroying him via Soul Suicide, which Yhwach would never be able to "see" coming since it's a death by Hollow.
Yhwach's "vision" and "interpretation" might be:
Ichigo appears -> ????? -> Yhwach standing over an (apparently?) dead Ichigo -> ?????
He interprets the first ????? as Ichigo doing "something" to thwart Almighty, but then assumes it's ultimately futile because of the "dead Ichigo" segment of the vision.
Then he possibly interprets the SECOND ????? as himself just DEACTIVATING Almighty because he's won, it's no longer "necessary," and he's fairly arrogant and considers his "foreknowledge" infallible.
When the "real" sequence of event would be:
Ichigo appears -> Ichigo activates Balanced Hollowfication and sacrifices himself -> Yhwach standing over an (apparently?) dead Ichigo -> Yhwach can no longer control Almighty and/or implodes due to Soul Suicide.