When I go into sandbox and press the respawn button in SE, the server crashes with an error. This is the only problem that makes me unable to install this mod on the server

I'll look into it, but why would you do that?

The problem is that it’s not me who can do it, but someone else.

I don't think that this mod has the capabilities to handle this situation properly. To be clear, SE is crashing on its own, there's no code in this mod that is wrong - they simply have assumptions that aren't true in this state.

While I can prevent the game from crashing by using some portions of their API, it doesn't actually produce a good state within the game, so it's not something I'd want to support.

In my opinion, the best solution involves SE either exposing an API for preventing/allowing respawning, or internally detecting this situation and preventing the respawn. This mod has no APIs of its own, but if they need some methods, I can create them.