Sharing resolve for new Owncloud server as follows.
- Owncloud 10.0.4
- Centos 7.4
- apache 2.4.12 updated to 2.4.29 (http/2)
- PHP 7.1.11
- APCu 5.1.8 (memcache.local)
- Redis 3.1.4 (memcache.locking)
- Intermittent blank page at login
- multiple page refresh to render pages
- PC and Android client "Connection closed"
- "failed to request notifications. Please try to refresh the page manually" notifications
- "Zend_mm_heap_corrupted" - multiple errors logged in httpd error_log
Resolution was to remark out [apc.serializer = "default"] in /etc/php.d/apcu.ini
Hope this helps someone.