I can't find that second reading in the text.

It's an admittedly very counter-intuitive reading.

This would only be a very loose analogy (and I actually have to run in a second, so I can't explain as much as I'd like), but... there was a rabbinic interpretation of Psalm 105:8 that concluded that the Law wouldn't be given until 1,000 generations (of humanity) had passed. Yet since only 26 actual generations passed before this happened, the rabbis had to come up with some story about the 974 generations "before" this. So they came up with

nine hundred and seventy-four generations . . . pushed themselves forward to be created prior to the creation of the world; yet they were not created. [God] went and placed them in every generation, and they form the arrogant that are in each generation.

Yet, really, this is just a cute little story. It's not literal -- or even sensible... as if a "generation" of humans could exist apart from human procreation (like a grin without a cat).

Of course, Paul's text is by no means in the same genre as the former. But I suppose people would suggest that it serves a similar rhetorical purpose while not actually being literal. (I know how problematic this all this; I'll try to address it later maybe.)

Are there any sources that indicate early Christians found the crucifixion to be a problem?

I mean, we maybe have a hint of this in places like Luke [24:21]... but we almost certainly shouldn't make too much of this.

What I'm really talking about is a very primitive pre-textual stage -- though, I mean, this is ultimately what caused the parting of the ways between Judaism and Christianity in the first place: that the former consider Jesus to be a failed messianic claimant, by virtue of his death and failure to inaugurate the messianic age. (Though Christians also had to deal with the failure of the eschaton to materialize -- an anxiety that we do find hints of in the New Testament.)