WLS cache and OVR not working

I have two WLS instances.

one on port 9977 and one on 9088, not that this is relevant - it just helps me paint the picture.

I restart both of them every night, as well as all of the BIPublisher WLS that runs OVR for me.

9977 has OVR working all of the time, everytime.

9088 is constantly "hit and miss".

What am I doing wrong?

If I redeploy an old tools release, 9088 will work for a couple of sessions and then stop.

So, I'm thinking temp files and cache at this stage.  Not the SM cache, as I'm restarting the thing nightly - longer term lower level WLS cache.

The type of cache that occupies directories like:

/u01/app/oracle/Oracle/Middleware/user_projects/domains/mydomain/servers/JDE91DV/tmp
/u01/app/oracle/Oracle/Middleware/user_projects/domains/mydomain/servers/JDE91DV/cache

There are files deep within this structure that are dated Dec 17 - when the instance was created!

So stop your managed instance (mine is called JDE91DV), so I run

/u01/app/oracle/Oracle/Middleware/user_projects/domains/mydomain/bin/stopManagedWebLogic.sh JDE91DV

delete the dirs
cd /u01/app/oracle/Oracle/Middleware/user_projects/domains/mydomain/servers/JDE91DV

then 
rm -Rf ./cache
rm -Rf ./tmp

I created dirs, don't think that you have to
mkdir ./cache
mkdir ./tmp
chmod 777 ./tmp
chmod 777 ./cache

then start up
/u01/app/oracle/Oracle/Middleware/user_projects/domains/mydomain/bin/startManagedWebLogic.sh JDE91DV


Now OVR is working like a treat - but for how long?