Whenever one uses ThermalDynamics Viaducts with AM2 and HEE installed it causes a crash (NullPointerException) and temporary world-corruption (the player is still in the viaduct on world load and thus causes an insta-crash for the same reason)(removing either hee or am2 and loading the world once without them allows you to leave the viaduct and thus preventing the crash).
It seems that your am2 handler is being triggered when TD turns the PlayerModel and takes temporary control of the camera.
If my suspicion is correct a try-catch block in the am2NullWorldConstructionWorkaround method should either fix the issue or at least return a 'clean' crash report.

Full crashlog: https://gist.github.com/Leguan12/a208e17d8a7fd12a4620350b17dcf0af
(HEE, AM2 and TD on latest version)

It helped, thanks 👍
You're also right regarding TDs use of an Entity - The viaducts use a dummy entity wich the player is riding to make it seem like the player would in fact be inside the pipe.

Disable the AM2 workaround with the IMC option in HEE config for the time being, and let TD know they may not be registering some entity they're spawning, if I understand what happened.

HEE:System:DisableIntegration { "modid": "arsmagica2" }

I'm having the same issue, but I can't figure out where to put the disable integration code to get it to actually work. Please let me know how to fix it.

http://hee-api.chylex.com/#basics (Implementing IMC using HEE configuration)

I tried to follow that, but I think I messed up somewhere along the way. I have exactly this in my config
general {
# List of IMC/API messages, documentation can be found on http://hee-api.chylex.com
S:IMC�<
Write your message here
HEE:System:DisableIntegration 1.8.1 PostInit { "modid": "arsmagica2" }
>
(Doesn't show the indenting in the comment and I'm not sure how to make it, but they have the same indentation as the Write your message here line)
in that section, and the tubes still crash my game every time. Additionally, it generates a .errored config file every time I try, but the log doesn't show any errors when I looked through it. Sorry if I messed up something simple here.

You're not supposed to copy the entire table, just the command and JSON. If you don't delete Write your message here, HEE will ignore the config. You also have some corrupted character after S:IMC.

AM2 workaround will be removed next update.