Was able to reproduce this with only Sandbox and Factorissimo installed.
If you go into a building inside sandbox, it lets you in like it always has.
But you can't get back out. No matter how carefully you line up, you're stuck inside.
Even went in (press W) and immediately pressed S to exit but was not able to leave the building.

That's Factorissimo's change, not this mod. Factorissimo also allows you to enter/exit via shift-right-clicking some of its entities.

Oooh shift right click! Thanks that works. It only moves your remote view, rather than your body, but in Sandboxes, you don't have a body anyway. Nice.

Though I just noticed that the electric grid from the sandbox doesn't make it into the factorissimo interior. Not sure if that's your end or his end. ;)
Workaround is to place an electric energy interface inside the building.

I also ran into the problem that the structure inside the sandbox does not let out of itself when you are in god mode in the sandbox, if you use the creative mod to exit god mode, then there are no problems getting out, but if I play on save where the creative mod is blocked, there is no way to disable god mode, it seems to me it would be convenient in the settings of the sandbox to be able to simply turn off the God mode function.

That is rather complicated, and ultimately it is not a problem or solution that this mod is involved in.

Besides, I already told you how Factorissimo changed and now allows you to enter/exit via Shift+Right-click its entities at the bottom/entrance of the factory. I just checked again to be sure: on a fresh game, with default settings except enable-all-technology, I can definitely enter/exit the factories using that method. It's better than trying to line up and walk in/out.

It worked in every case I tried it in, whether as the God or Remote View, or the God using Remote View.

Thank you for answer. It's really better than nothing.