Backup App not working

In the sidebar I get the message
"The following can be backed up
• Files
• MySQL Database".

When trying to backup "Database only" I get an ZIP as usual, but the SQL file in it is empty.
When trying to backup "Database and entire CMS folder" I get a blank page in the browser.

Apart from that I can use Perch as usual. New content is saved to the database and can be retrieved to be displayed in frontend and backend.

Here's my extended report:

    Perch: 2.8.18
    Production mode: Production (100)
    Installed apps: content (2.8.18), assets (2.8.18), categories (2.8.18), perch_forms (1.7), perch_mailchimp (2.0.1), perch_backup (1.2)
    DB driver: PDO
    DB tables: perch2_categories, perch2_category_counts, perch2_category_sets, perch2_content_index, perch2_content_items, perch2_content_regions, perch2_events, perch2_events_categories, perch2_events_to_categories, perch2_forms, perch2_forms_responses, perch2_mailchimp_campaigns, perch2_mailchimp_history, perch2_mailchimp_log, perch2_mailchimp_stats, perch2_mailchimp_subscribers, perch2_navigation, perch2_navigation_pages, perch2_page_templates, perch2_pages, perch2_resource_log, perch2_resource_tags, perch2_resources, perch2_resources_to_tags, perch2_settings, perch2_user_privileges, perch2_user_role_privileges, perch2_user_roles, perch2_users
    Users: 2
    App runtimes:

    <?php
        include(PERCH_PATH.'/core/apps/content/runtime.php');
        include(PERCH_PATH.'/addons/apps/perch_forms/runtime.php');
        include(PERCH_PATH.'/addons/apps/perch_mailchimp/runtime.php');
    ?>

    Scheduled tasks for perch_mailchimp: update_list_stats (60 mins)
    Editor plug-ins: markitup
    H1: cf7c8ed8f6f7b960370641191b30af1f
    L1: f89a22b29e398d41df6045df92b75662
    headerColour: #454545
    content_singlePageEdit: 0
    helpURL:
    siteURL: /
    hideBranding: 1
    content_collapseList: 0
    lang: de-de
    update_2.4.9: done
    latest_version: 2.8.15
    on_sale_version: 2.8.18
    headerScheme: dark
    content_hideNonEditableRegions: 1
    dashboard: 0
    hide_pwd_reset: 0
    content_frontend_edit: 0
    logoPath: /p/resources/1400141012_Logo.png
    perch_events_update: 1.8
    perch_backup_mysqldump_path:
    perch_events_detail_url: /events/event.php?event={eventSlug}
    perch_mailchimp_secret: ***
    perch_mailchimp_update: 2.0
    perch_mailchimp_api_key: ***
    perch_mailchimp_list_id: ***
    perch_mailchimp_campaign_url: /mailchimp/campaign.php?s={campaignSlug}
    update_2.6.3: done
    update_2.7.4: done
    update_2.7.8: done
    update_2.8.18: done
    PERCH_DEVELOPMENT: 10
    PERCH_STAGING: 50
    PERCH_PRODUCTION: 100
    PERCH_DB_USERNAME: ***
    PERCH_DB_SERVER: ***
    PERCH_DB_DATABASE: ***
    PERCH_DB_PREFIX: perch2_
    PERCH_TZ: Europe/Berlin
    PERCH_EMAIL_FROM: ***
    PERCH_EMAIL_FROM_NAME: ***
    PERCH_LOGINPATH: /p
    PERCH_PATH: ***
    PERCH_CORE: ***
    PERCH_RESFILEPATH: ***
    PERCH_RESPATH: /p/resources
    PERCH_HTML5: 1
    PERCH_DEBUG: 1
    PERCH_RUNWAY:
    PERCH_ERROR_MODE: DIE
    PERCH_DATE_LONG: %d %B %Y
    PERCH_DATE_SHORT: %d %b %Y
    PERCH_TIME_SHORT: %H:%M
    PERCH_TIME_LONG: %H:%M:%S
    PERCH_PREVIEW_ARG: preview
    PERCH_TEMPLATE_PATH: ***
    PERCH_DEFAULT_DOC: index.php
    PERCH_DEFAULT_EXT: .php
    PERCH_PRODUCTION_MODE: 100
    PERCH_RWD:
    PERCH_HTML_ENTITIES:
    PERCH_SSL:
    PERCH_STRIPSLASHES:
    PERCH_PROGRESSIVE_FLUSH: 1
    PERCH_AUTH_PLUGIN:
    PERCH_DB_CHARSET: utf8
    PERCH_DB_PORT:
    PERCH_DB_SOCKET:
    PERCH_SESSION_TIMEOUT_MINS: 20

Hosting settings

    PHP: 5.6.13
    Zend: 2.6.0
    OS: Linux
    SAPI: cgi-fcgi
    Safe mode: not detected
    MySQL client: 5.5.44
    MySQL server: 5.5.45-3
    Extensions: Core, date, ereg, libxml, openssl, pcre, sqlite3, zlib, bcmath, calendar, ctype, curl, dom, hash, fileinfo, filter, ftp, gd, gettext, SPL, iconv, session, json, mbstring, mcrypt, mysql, mysqli, pcntl, PDO, pdo_mysql, pdo_sqlite, standard, posix, Reflection, imap, SimpleXML, soap, sockets, Phar, exif, tidy, tokenizer, xml, xmlreader, xmlrpc, xmlwriter, xsl, zip, cgi-fcgi, mhash
    GD: Yes
    ImageMagick: No
    PHP max upload size: 50M
    PHP max form post size: 50M
    PHP memory limit: 128M
    Total max uploadable file size: 50M
    Resource folder writeable: Yes
    Session timeout: 24 minutes
    Native JSON: Yes
    Filter functions: Yes
    Transliteration functions: No
    PATH: /usr/local/bin:/usr/bin:/bin
    PHP_FCGI_MAX_REQUESTS: 10000
    HTTP_MOD_REWRITE: On
    PHPRC: /home/***
    USER: ***
    GROUP: ***
    ORIG_SCRIPT_NAME: /fastcgist/php5.6
    ORIG_PATH_TRANSLATED: ***
    ORIG_PATH_INFO: /p/core/settings/diagnostics/index.php
    ORIG_SCRIPT_FILENAME: /usr/local/fastcgi-starter/php5.6
    SCRIPT_NAME: /p/core/settings/diagnostics/index.php
    REQUEST_URI: /p/core/settings/diagnostics/?extended
    QUERY_STRING: extended
    REQUEST_METHOD: GET
    SERVER_PROTOCOL: HTTP/1.1
    GATEWAY_INTERFACE: CGI/1.1
    REDIRECT_URL: /p/core/settings/diagnostics/index.php
    REDIRECT_QUERY_STRING: extended
    REMOTE_PORT: 50752
    SCRIPT_FILENAME: ***
    SERVER_ADMIN: [no address given]
    DOCUMENT_ROOT: ***
    REMOTE_ADDR: ***
    REMOTE_HOST: ***
    SERVER_PORT: 80
    SERVER_ADDR: ***
    SERVER_NAME: ***
    SERVER_SOFTWARE: Apache
    HTTP_CONNECTION: close
    HTTP_COOKIE: PHPSESSID=***; cmsa=1
    HTTP_REFERER: ***
    HTTP_ACCEPT_ENCODING: gzip, deflate
    HTTP_ACCEPT_LANGUAGE: de,en-US;q=0.7,en;q=0.3
    HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
    HTTP_USER_AGENT: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:42.0) Gecko/20100101 Firefox/42.0
    HTTP_HOST: ***
    suexec_memlimit: 310
    suexec_cpulimit: 10
    PHP5_EXT: .php .php5 .phtml .phps
    suexec_timeout: 90
    PHP_EXT: .php4 .php3
    REDIRECT_STATUS: 200
    REDIRECT_HANDLER: php-fastcgi5.6
    REDIRECT_suexec_memlimit: 310
    REDIRECT_suexec_cpulimit: 10
    REDIRECT_PHP5_EXT: .php .php5 .phtml .phps
    REDIRECT_suexec_timeout: 90
    REDIRECT_PHP_EXT: .php4 .php3
    FCGI_ROLE: RESPONDER
    PHP_SELF: /p/core/settings/diagnostics/index.php
    REQUEST_TIME_FLOAT: 1449833966.4735
    REQUEST_TIME: 1449833966