nfs problem with php session directory

I share /var/lib/php/session among 2 servers

everything works fine except this morning I checked my server and the
client machine had /var/lib/php/session described like this:

drwx------ ? ? ? ? ? session

session was also flashing in bash.

I dont remember all the places that had question marks, but most had em
including user and group id. when I went on my website, I had some
error that it couldnt write in that directory.

what caused this, I fixed it by remounting this nfs path but I dont
want this to happen and if it does I want it to fix automaticly.

any idea?

thank you.