I know this mod is pretty much dead, and that it hasn't been updated for about 4 months now, but this crash may be important to you:
https://paste.dimdev.org/jopixikeke.mccrash
Armory Expansion, Construct's Armory, and Tinker's Construct are all latest version, and I believe that may be the cause.

@NyanMC any further info about this? Did you ever manage to reproduce this?

Please don't make assumptions, this mod very much is not dead, the author has been busy for a while, and the current state of world affairs has made things even less of a priority.

That said, your issue looks to be to do with one of the json files related to conarm and applied energistics as noted in the crash:

Caused by: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 1 path $
at com.google.gson.Gson.fromJson(Gson.java:899)

I don't however know which json file.

@NyanMC what mods and versions are you running? have you made any changes to the conarm-materials.json file in the config folder?

It should list every single mod in the crash log, but for specifics, here's the mods that could relate to this in any way:
Armory Expansion is on 1.4.1
Mantle is on 1.3.3.55
The only mod I use this on is Ice and Fire (on version 1.8.4)
Construct's Armory is on version 1.2.5.4 (considering the exception was from armory expansion - construct's armory, i would not be surprised if an update to conarm broke the whole thing)
Tinker's Construct is on 2.13.0.183
In case PlusTIC has something to do with this (doubtfully, but you never know), that's on 7.1.6.1

While I couldn't reproduce the crash, have you tried deleting the config/armoryexpansion/conarm folder and it's contents?

now that i think about it, when i got the crash it was also on a corrupted world that i didn't know was corrupted until i removed about 5 mods. i'll try with a fresh world and mention if i still get crashes.