Já aconteceu comigo em meu vps e só conseguir resolver da seguinte forma:
If you have root access (VPS or dedicated server), look for this value by typing at an SSH prompt:
grep -i rlimit /usr/local/apache/conf/httpd.conf
If there is a value, e.g. RLimitMEM 55924053, comment it out with “# ” and restart Apache.
This fixed my problem and might help others. Be sure to backup php.ini before you try this.