PHPUnit code coverage hangs on functional tests

My tests run fine when not using --coverage-text, but they hang on the functional tests that extend BrowserTestBase indefinitely when using coverage.

Here's my config file:

<?xml version="1.0" encoding="UTF-8"?>
<phpunit colors="true"
         beStrictAboutTestsThatDoNotTestAnything="true"
         beStrictAboutOutputDuringTests="true"
         beStrictAboutChangesToGlobalState="true"
         checkForUnintentionallyCoveredCode="false">
  <php>
    <ini name="error_reporting" value="32767"/>
    <ini name="memory_limit" value="-1"/>
    <env name="SIMPLETEST_BASE_URL" value="http://d8.dev"/>
    <env name="SIMPLETEST_DB" value="mysql://root@localhost/dev_d8"/>
  </php>
  <testsuites>
    <testsuite name="unit">
      <file>./UnitTestSuite.php</file>
    </testsuite>
  </testsuites>
  <listeners>
    <listener class="\Drupal\Tests\Listeners\DrupalStandardsListener">
    </listener>
  </listeners>
  <filter>
    <whitelist addUncoveredFilesFromWhitelist="false">
            <directory>../../docroot/modules/custom</directory>
      <exclude>
        <directory suffix="Test.php">../../docroot/modules/custom</directory>
        <directory suffix="TestBase.php">../../docroot/modules/custom</directory>
      </exclude>
    </whitelist>
  </filter>
</phpunit>