Strange infill separation problem after pretty good first layer

Seeing this issue trying to print a v-chonk base. First layer isn’t flawless but looks pretty ok at least to me. Second layer even starts ok…but then at some point midway through that second layer the lines just start lifting up and separating from each other.

Second time this has happened. First time it happened I figured I’d up my extrusion multiplier to make sure enough plastic was going down. I also went ahead and dehydrated the filament for about 7 hours at 60. Unfortunately those changes didn’t do a thing.

VC3.1, Polymaker ABS, 100 on the bed and 260 on the nozzle. 1.0 extrusion multiplier (was 0.92 on my first attempt). I’m struggling to understand what sort of issue would cause this kind of behavior. Can anyone who’s seen behavior like this before ELI5 a plausible explanation of what might be happening here?