We're experiencing a problem in Moodle 2.9.1 which may or may not be the same as this problem.
For us, intermittently (about once a month on a fairly heavily used site) we lose TinyMCE altogether- in all browsers - until we can restart Apache.
When this issue occurs, we see lines in our server's error_log file like this:
[Tue May 24 09:17:57.409754 2016] [:error] [pid 4196:tid 140101959018240] [client 209.121.121.254:49625] PHP Fatal error: Call to undefined function define() in /var/web/wwwroot/moodle/lib/editor/tinymce/plugins/loader.php on line 32, referer: http://moodle.royalroads.ca/moodle/mod/forum/post.php?reply=1289344
So a core PHP function, define(), is no longer defined.
This issue resolves if we restart Apache or if we disable all TinyMCE plugins in the Moodle UI. Re-enabling any plugin brings the issue back. If we restart Apache (and thus PHP) the issue resolves for up to a month, even with all plugins enabled.
Memory usage on the server is normal (lots free) when this issue is occurring, and we have tried giving PHP more memory, to no avail.
Has anyone experiencing the issue in this discussion also seen symptoms like these?