PPPoE strange problem, hw or sw

Hello, I notice a strange problem that occoured after ROS upgrade.
I had pppoe on any NAS made with RB2011, NAS core router, on these routers I have two or tree interface used for backbone link, the others are bridged. AP are connected to bridge, route are managed by OSPF, 2 radius servers manage any pppoe user on the network.
This configuration works since ROS 6.1 so, I upgrade ROS and firmware on the RB2011.
Now users connect and disconnect rotating, all users connected to that NAT.
I try to downgrade again also to 5.25 (fw and ros) but the problem remain. Today I had made this upgrade on a router that after one year of work seems became slow also after multiple reboot.
Results: users that were “rock authenticated” (no disconnection and reconnection on log file) now reconnect any few minutes but RB2011 became wery fast.
What’s happening? Any other users had the same problem? Any solution?
I had made search on forum but seems that this problem is only on my net.

Thank you for any infos or suggestion