I have a similar issue, the game will load infinitely, however, this will happen only with RotC for SS2 enabled. I have currently installed SS2, Chapter 2, the MEGA city plan contest pack, loads of addons (like: pra's random addon, ruined homes, superstructures, Favelabulous, etc.) XDI with the patch, FO4SE and so on. Without the RotC the game loads within seconds, with RotC it seems the game ??freezes??, meaning the loading icon still moves, music plays and whatever graphic does its animation but nothing happens.
I have done experiments with my 8h save (I tried to add RotC later) and with a new game, with RotC save game never loads, without RotC game loads within seconds. Also, I have done a clean install to the game, but with no changes.
Tho, I am using Vortex to manage my mods. Maybe it causes problems?? Like, wrong mod order, etc
Otherwise, I do not know how to solve this problem, although I really would like to use RotC larger city plans.
I don't think that my system is the bottleneck here:
CPU: AMD 5800X
RAM: 32GB
game drive: NVME SSD
GPU: NVIDIA 3090