Hi Josè,
that is not the configuration I'm talking about: I'd like to read your plain php.ini settings about opcache i.e what described in https://docs.moodle.org/29/en/OPcache#Configuration.
strace will be the key to understand what is broken in your environment: there are many clusters out of there running MUC on a file system shared between the front-end nodes and happy with opcache.
As Howard told, it could be a library but to find the culprit you need to go into the internals of the broken requests: it's time consuming and stressing but when you'll find the root reason your patience will be rewarded.
You could also post the configuration of the NFS mount point (assuming that it is equal for each front-end node): see here an example, https://moodle.org/mod/forum/discuss.php?d=310501.
HTH,
Matteo