When teleporting over long distances, there's a good chance that the game will crash. Here's one crash log among many: https://pastebin.com/U844A9LN

After teleporting ~50 times 10k blocks or more I can't reproduce this crash.

1. Does it happen with only TFC installed?
2. If so, what specific steps are you doing that causes a crash (world, tp, seed, etc.)

Yes
Teleport anywhere, then move about 10-16 steps away from your current location using whatever randomly generated seed the world gave you. The crash isn't 100% guaranteed to happen, but when it does, you'll usually crash 1-3 more times upon logging back in and trying to move forward
New crash log with only TFC installed: https://pastebin.com/kDMxjb2i
2nd crash log upon logging back in and attempting to move forward 1 block: https://pastebin.com/hYcLa6Ef

I can't reproduce this, (I've tried many times, in addition to the same world that crashed you, with the same teleport coordinates.) nor do I see any reason why that crash would be happening. Do you have a specific world / seed / teleport location that is guaranteed to crash for you? Because I have no way to fix this if I can't make it happen.

Nah, it seems to be entirely random for me. Also, I'm using Forge v14.23.5.2768. Could that have anything to do with it?

That is the forge version that we are using as well. This is driving me bananas

And if it helps narrow things down, I've been experiencing this crash since early September of 2018, so the crash isn't being caused by any recent changes

So, I actually get this crash every now and then on initial worldgen in my dev environment.
crash-2019-04-17_15.39.28-server.txt

So I have absolutely no idea what is causing this. I still haven't experienced it myself, despite a lot of trying. If it has a specific cause, it is buried under layers of GenLayerTFC and other worldgen nonsense that is probably going to be re-written anyway for 1.14. I am going to attempt to stop the crash without actually fixing the bug, hopefully it will be useful and then maybe it can be fixed layer or during rewrites.

Edit: it annoys me that I can't just reproduce with with seed + location, because that means there is a non-deterministic bug in worldgen somewhere as well

So I think I have ducktape fixed this, I'm closing unless it can be produced again. Re-open this issue if it is still a problem