apt.wikimedia.org contains php-xdebug 2.7.0 which is utterly broken (see T247587 and T263930). 2.7.2 fixes the heap of performance bugs which cause those issues. Please update the apt.wikimedia.org package.

There is T220406: Package XDebug 2.9 for apt.wikimedia.org but it has been in limbo for over a year, this issue is breaking one of the more commonly used Wikimedia developer environments, and presumably updating to 2.7.2 is simpler (2.9 requires updates to some other PHP packages; 2.7.2 doesn't).