Rendering Twig template returns "cache is corrupted" and outputs PHP code

I'm attempting to render out a Twig template that has no layout, just a few variables and some loops.

When I call the render() function on Twig, it outputs a block of PHP code for the following class:

php
/** path/to/my/template.html.twig */
class __TwigTemplate_435244378aba3a3f94258b7d2af4d53eb7a41acb741dd3ad0efcac038b621c67 extends Twig_Template
{
    // bunch of methods for Twig_Template, 
    // including the compiled version of my template
}

After this it gives me a stack trace with the following exception:

Failed to load Twig template "path/to/my/template.html.twig", index "": cache is corrupted in "path/to/my/template.html.twig".

I'm not even using a cache with this app currently, though adding a cache doesn't seem to make a different. I'm using Twig like this:

// Factory to return a new Twig environment
$loader = new \Twig_Loader_Filesystem(__DIR__ . '/../../views/');
return new \Twig_Environment($loader);

// My class has $this->twig set to the above object
$this->twig->render('path/to/my/template.html.twig', [
    'report' => $report, 
    'file' => $file
]);

Twig seems to be able to read in my template, as the block of PHP code it outputs in the error has a properly compiled version of the template. Attempting to set a cache directory that is writable still results in the same error.

I'm using Twig 1.34.4 and PHP 5.6.29 under Apache.

EDIT

A bit of success, in a way. It seems that Twig is never evaling the code that it's generating.

I edited the vendor/twig/twig/lib/Twig/Environment.php file and on line 448 added the following:

eval("?><?" . $content);

After that my template renders just fine. That leads me to the conclusion something else in Twig is breaking, but this isn't a long-term solution since I shouldn't be editing the vendor files.

The block starting at line 456 seems to indicate that $content should have the opening <? but mine doesn't. So that could be screwing with the compilation.

Time for more digging.