[alex.sk]

I have a strong impression part of this thread is missing.

I meant init_startup hook from datastore. I.e. the piece of eval()'d code where line 466 happens to be.
Unless you have better ideas, something like

if($_GET['dumpinitstartup']) var_dump(vBulletinHook::fetch_hook('init_startup'));

right before line 336

($hook = vBulletinHook::fetch_hook('init_startup')) ? eval($hook) : false;

in includes/init.php, and then calling http://your/board/index.php?dumpinitstartup=1 should show you that code.

Because afaik both of those are vanilla, aka untouched.

That would be really strange. Line 466 in this plugin alone is nowhere near any user-defined functions.
In any case, with errors like this, I'd try to avoid any guesswork and make sure it's clear where exactly it happens.