Seems like the DEF bones spine_01 and spine_02 have an additional bone constraint "Copy Rotation.001" (that seem to not provide any additional functionality?) and they seem to be targeting tweek_spine.002 and tweek_spine.003 respectively.
(Maybe this is intentional and I am missing something, but they are screwing up my rigs, and they seem to work perfectly when disabling those 2 extra constraints)
I noticed this too recently after the changes from the recent update. I had to shuffle some constraints around to fix other spine problems. I'll dig into it and find a fix that doesn't break other fixes haha.
Drat so these constraints you've mentioned are the very specific ones we added to solve a larger spine deformation problem the former versions had, check the screenshots to see the issue.
https://felesmachina.itch.io/rigodotify/devlog/1580130/rigodotify-v240-is-live
Formerly there was a limit_scale constraint on those bones coming from the original Rigify , BUT those ones ended up really mucking up the spine when arching the upper back or abs (see the post photos). Swapping to the rotation constraints gave MUCH more natural back arch but yeah, it seems they slightly offset the base pose position. I'll try to tweak it further to keep the base pose the same.
