Sorry, I'm kinda having a deja vu or something right now because I don't really remember posting here, but I guess that's because of COVID brain getting to me. Been locked inside so long can't even remember which day comes after which.
Luckily I'm remembering now, so I can get help on this issue and hopefully help someone else out if they are having the same issue.
So, the redstone contraption I know wasn't the problem because the world would crash on load. It wasn't a build error, it was something wrong with the world itself. Notably, all of the "strange" world generators such as "void islands" and "void" and others would fail like this, and this has not resolved with the new patch (since I have played KM since the earlier Theta release in early 2020.)
Also notably, adding a mod to the game to make the world did not have the same effect (I don't like doing this though 'cause it could break the balance of the 500 mods, but I have tested it.) Loading a normal world and then loading a void portal through a void dimension mod did not crash the game.
I don't believe I have a crash report for the world in my files yet because I opened a new folder on MultiMC for the September update twice, and the folder I currently use I haven't generated a void world in yet. But I can certainly do that! I will try to get the file to you shortly in Discord, and hopefully this is something that can be fixed.