Something that is immeasurable can become measurable when something comparable comes along. The Earth is immeasurable to a kid with a ruler, but they can still comprehend Jupiter's size when told its volume is worth over 1,000 Earths.
Perhaps Kaguya's powers are way more intense, denser, burning Naruto's eyes/senses maybe, in a way the Juubi's never did. It's clear the difference in power is obvious to him.
I'm saying the word "immeasurable' should not be given too much focus given that it's a translation. The Kyuubi is also a living being with a personality and completely capable of using figures of speech.
Plot hole or not, this is just petty. This "hole" is insignificant. All you needed to get from this was that Kaguya was stronger than the juubi. There is no need to focus on petty details that Kishi probably just wasn't thinking about at the time.
Kurama said that the Juubi can't be sensed BECAUSE ... and then he essentially explains that it's because it is made of natural energy. He didn't say "The Juubi can't be sensed, PERIOD" which is what it looks like you're telling us in your post.
Then Kurama said, "It's a bit different if you do it in Hermit Mode." Next panel, Naruto is shows that he understands that the reason that it can't be sensed is because it's Nature Energy (Naruto was paying better attention to the kyuubi than you). Normal people can't sense Nature Energy. He can sense Nature Energy in Sage Mode. Seriously the explanation for why Naruto can sense the Juubi is on the very page you shared.
Naruto is the one making the comparison between Kaguya and the Juubi. Duh, the one who had the ability to sense the Juubi before is the one with the ability to compare them. And he is comparing them.
Naruto is using Sage Mode right now. You can tell because he has cross pupils. The horizontal bar is the Sage Mode part.
Naruto & Sasuke were too weak at the moment too sense it.
Now they are basically like the Sage's son which makes them on par with fighting the Juubi and they are more powerful which makes them sense the "Immeasurable" power.
Naruto & Sasuke were too weak at the moment too sense it.
Now they are basically like the Sage's son which makes them on par with fighting the Juubi and they are more powerful which makes them sense the "Immeasurable" power.