Required PHP Modules

I’m testing my site with PHP7 and your nice plugin will not regenerate any images. I think I missed some modules, because it looks fine. There is no error message within the error.log.

"Featured" (ID 22414)

BaseDir: /var/www/efr/wp-content/uploads
BaseUrl: http://10.11.12.13/wp-content/uploads
Image: /var/www/efr/wp-content/uploads/2015/10/Featured1.jpg

Currently installed PHP modules:

bcmath
calendar
Core
ctype
date
dba
dom
enchant
exif
fileinfo
filter
ftp
gettext
gmp
hash
iconv
json
libxml
mbstring
mcrypt
mysqli
mysqlnd
openssl
pcntl
pcre
PDO
pdo_mysql
Phar
posix
Reflection
session
SimpleXML
soap
sockets
SPL
standard
sysvmsg
sysvsem
sysvshm
tokenizer
xml
xmlreader
xmlwriter
xsl
zip
zlib

https://wordpress.org/plugins/regenerate-thumbnails/