This one is quite old. I took at look at this in our system and see that for the specific issue described by this PD/CR, that the error that customer was seeing was not related to any software bug. In that case, the customer's switch was over limits for routes and IPMC cache.
The notes in the PD/CR are summarized as follows:
After re-testing this PD under normal scaling limit against build 12.5.x there is no error any more. I have decided to close it. As an aside - this may be ok as I see that you have 22K routes, > 1600 IPMC caches, and > 4000 cached remote hosts so slot 1 is a bit above normal scaling limits (12000 routes, ~6000 IPMC caches + hosts).
Unfortunately, the specific log message shared doesn't give us enough information to the nature of the issue in your network. Can you share with us the EXOS version, hardware model(s), and some additional log messages that may be around the "Entry not found?"
Also, take a look at this knowledge article to see if it helps provide you with some more information:
https://gtacknowledge.extremenetworks.com/articles/Solution/Unable-to-Add-L2/