I'm having the same problem when I get the dialogue Pidgeon shared while Jennifer is going over the posing tutorial. If I accept the tutorial, I get the error after she introduces HAPPY POSING. If I turn down the tutorial, it skips straight to the error. The full error screen calls some different values, but it resolves with the same 'I_who1' not being defined.
I'm on Windows 10. I have gotten every update that the Windows updater is offering. I tried lowering the game's resolution, but that didn't change anything.
I have used the companion mod to max the MC's stats and to increase max affection and love for the girls (except for Amy) to 100. Also used the app to change the subdermal implant levels from 1 to 3 after I get them and added a bunch of stuff to my inventory. I removed the companion mod file to try without it, but got the same result, so I've put the file back.
Gonna see about installing/updating the softwares mentioned to see if things change.