60fps Issue, Premiere pro, A7IV 10-bit? 4k?

Okay so i shoot and edit alot of weddings, i recently got my self an A7IV and i shoot 10-bit 4k HS setting in camera for my weddings, i also occasionolly will pop into 1080 as the a7IV has a crop when shooting 4k 60

I'm setting these clips into a 1920x1080 timeline in 23FPS, and slowing them down to 40% to acheive a slow motion effect.

now for some clips this works great! some (1080 and some 4k) but for others they're looking ...choppy? as if it's playing at 15fps, and for some reason the only fix i can find for this which makes no sense is nesting each "bad" clip in a 60fps nested sequence. and then they play back okay in my main timeline. (but also sometimes they don't and i have to change the nest to 59fps instead of 60fps?)

and belive me i've checked my shutter speed, all clips were shot at 1/125, and the real kicker is that the issues presists even on export. 

this is using premiere 2023, latest version. i've had this issues across 2 differend PC setups aswell.

even tried a firmware update on my camera as a friend had suggested this, (he told me he's had a similar issues)

i'm stumped on this one, i have my work around for it but if anyone could explain why the problem is here in the first place it would be greatly apprciated as this is wearing on my sanity.