Registered just to tack on to Nearox, Sacralletious, and Irregulator have been mentioning about worldspace edits. As a preface, I haven't yet tried STEP, but use a mish-mash of it's mods and GEMS to provide my setup. I have been using the Immersive Patrols, Immersive Creatures, OBIS, and the Populated Roads and Cities mod collection. I know I shouldn't have gone over the 2-3 mod spawn limit, but I think I've finally found a stable build using this worldspace tweak. But by deleting the worldspace edits that Immersive Creatures adds directly from the esp files using TES5Edit, I've hopefully built a less crashing setup. I originally couldn't go an exterior cell or two without a CTD, and now, running the short distance from outside Whiterun to its doors have not caused a crash, and Papyrus logs are at tiny amount of around 75KB. Finally going to start playing and see where this takes me :D
I hope this actual account helps others until v7 comes out.
EDIT: Playing with the worldspaces removed from SIC gives me a good hour or more of playtime until any glitches start to arise, specifically when accessing menus. Graphical glitches start to show up, but Skyrim Performance Monitor shows the game holding steady. Did not have a crash but had to kill the game from the Task Manager. I'll be turning on logging to see if it shows me anything. Also, I have invisible weapons, possibly from Immersive Weapons, but that's another problem for another day.
EDIT: Immersive Creatures was still crashing after worldspace edits. It just looks like I'll need to pare down my spawning mods to alleviate this mess. Checking now to see if it works without the mod. Also, I get graphical corruption on menus when SIC is installed: https://imgur.com/BYNIPb5,pvYIp3a#0