TF2 update news show a new post about matchmaking. It does not explicitly address our issue but I was curious if they fixed the bug. So I started TF2 on my main account and it seems to work just fine. I guess Valve fixed it without releasing a client update?

Here is a list of files that change when I start the game with my alt account.

tf/
├── cfg/
│   ├── config.cfg
│   ├── motd_entries.txt
│   └── server_blacklist.txt
├── download/
│   └── sound/
│       └── sound.cache
├── sound/
│   └── sound.cache
├── custom/
│   └── workshop/
│       └── sound/
│           └── sound.cache
├── streams/
│   └── *not important* 
├── scripts/
│   └── items/
│       ├── items_game.txt
│       └── items_game.txt.sig
├── stats.txt 
├── gamestate.txt
├── voice_ban.dt
├── tf2_misc.vpk.sound.cache
├── tf2_textures.vpk.sound.cache
└── modelsounds.cache

Given the fact that TF2 crashes with the same error on 3 different operating systems - all with a clean new installation of the game - makes me wonder if Steam stores a corrupted version of the item schema file which then gets propagated to the client, making the game crash for these specific Steam accounts. Since the file is digitally signed we can't make changes to it anyway. I don't really know what the problem is, just making blind assumptions lol.

At this point there is nothing you can do. It's a bug in the game's core, not caused by corrupted files. Probably has to do with our matchmaking level or backpack (I don't know what else would be different when using an alt account). I've tried everything I could possibly do. I even tried to play the game on 3 different computers, running Linux, Windows and OS X. I get the same error on all systems. I think this problem is tied to our accounts and we have to wait for Valve to fix it.

Your desired sidebar name: Flow
Country of residence: Germany
Twitch profile link: https://www.twitch.tv/floeplays
TF2 league profile page: http://etf2l.org/forum/user/34721/

Played in premier division, won sniper of the season award :)
I'm gonna stream scrims, pugs, officials in ugc plat and etf2l prem.