`ErrorLog` of site contains
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x790cb)[0x7f8d395fb0cb]
/lib/x86_64-linux-gnu/libc.so.6(+0x8421e)[0x7f8d3960621e]
/lib/x86_64-linux-gnu/libc.so.6(__libc_malloc+0x54)[0x7f8d39607de4]
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2(ConstantString+0x2a)[0x7f8d1e6945aa]
/usr/lib/x86_64-linux-gnu/ImageMagick-6.8.9/modules-Q16/coders/gif.so(RegisterGIFImage+0x69)[0x7f8cf5a8c669]
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2(+0x12a351)[0x7f8d1e61a351]
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2(OpenModules+0x69)[0x7f8d1e61afd9]
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2(GetMagickInfo+0x1b0)[0x7f8d1e615930]
/usr/lib/x86_64-linux-gnu/libMagickCore-6.Q16.so.2(GetMagickList+0x68)[0x7f8d1e6160e8]
/usr/lib/x86_64-linux-gnu/libMagickWand-6.Q16.so.2(MagickQueryFormats+0x20)[0x7f8d1ea4d430]
/usr/lib/php/20151012/imagick.so(zim_imagick_queryformats+0x66)[0x7f8d1ecf19e6]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_internal+0x15e)[0x7f8d27199e7e]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6af0)[0x7f8d2f901af0]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6c2d)[0x7f8d2f901c2d]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6c2d)[0x7f8d2f901c2d]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(+0x2e2e5c)[0x7f8d2f90de5c]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(zend_call_function+0x80f)[0x7f8d2f86e24f]
/usr/lib/apache2/modules/libphp7.0.so(zif_call_user_func+0xb5)[0x7f8d2f7babc5]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_internal+0x15e)[0x7f8d27199e7e]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6af0)[0x7f8d2f901af0]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6c2d)[0x7f8d2f901c2d]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(+0x2d6c2d)[0x7f8d2f901c2d]
/usr/lib/apache2/modules/libphp7.0.so(execute_ex+0x1b)[0x7f8d2f8bce9b]
/usr/lib/apache2/modules/libphp7.0.so(dtrace_execute_ex+0x198)[0x7f8d2f86c568]
/usr/lib/php/20151012/xdebug.so(xdebug_execute_ex+0x2ef)[0x7f8d271994ef]
/usr/lib/apache2/modules/libphp7.0.so(zend_execute+0x1a7)[0x7f8d2f910dd7]
/usr/lib/apache2/modules/libphp7.0.so(zend_execute_scripts+0xd3)[0x7f8d2f87c823]
/usr/lib/apache2/modules/libphp7.0.so(php_execute_script+0x2d0)[0x7f8d2f81cb20]
/usr/lib/apache2/modules/libphp7.0.so(+0x2e773a)[0x7f8d2f91273a]
/usr/sbin/apache2(ap_run_handler+0x40)[0x564ed7a905a0]
/usr/sbin/apache2(ap_invoke_handler+0xb6)[0x564ed7a90b26]
/usr/sbin/apache2(ap_process_async_request+0x372)[0x564ed7aa7fc2]
/usr/sbin/apache2(ap_process_request+0x10)[0x564ed7aa8170]
/usr/sbin/apache2(+0x6923e)[0x564ed7aa423e]
/usr/sbin/apache2(ap_run_process_connection+0x40)[0x564ed7a9a510]
/usr/lib/apache2/modules/mod_mpm_prefork.so(+0x37e9)[0x7f8d304837e9]
/usr/lib/apache2/modules/mod_mpm_prefork.so(+0x3a74)[0x7f8d30483a74]
/usr/lib/apache2/modules/mod_mpm_prefork.so(+0x3aeb)[0x7f8d30483aeb]
/usr/lib/apache2/modules/mod_mpm_prefork.so(+0x4ac7)[0x7f8d30484ac7]
/usr/sbin/apache2(ap_run_mpm+0x4e)[0x564ed7a74abe]
/usr/sbin/apache2(main+0x9b0)[0x564ed7a6e160]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f8d395a23f1]
/usr/sbin/apache2(_start+0x29)[0x564ed7a6e259]
complete log attached.
Removal of `php-imagick` works around the issue.
ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: apache2-bin 2.4.18-2ubuntu4
ProcVersionSignature: Ubuntu 4.8.0-26.28-generic 4.8.0
Uname: Linux 4.8.0-26-generic x86_64
NonfreeKernelModules: openafs zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.3-0ubuntu8
Architecture: amd64
Date: Tue Nov 8 12:02:20 2016
InstallationDate: Installed on 2015-04-20 (567 days ago)
InstallationMedia: Ubuntu-Server 14.10 "Utopic Unicorn" - Release amd64 (20141022.2)
ProcEnviron:
TERM=screen.xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=de_DE.UTF-8
SHELL=/bin/bash
SourcePackage: apache2
UpgradeStatus: Upgraded to yakkety on 2016-10-19 (19 days ago)
Based upon the backtrace, I think this might actually be a fault in imagemagick?