We have arround 500 users all together, there are 170 connected over PPPoE at this moment and
we use mikrotik only as access concetrator/pppoe server.
What happens is that occasionally one or two users falls out of the profile limit they have.
For example, user have 512/128 kbit profile assigned but for some reason mikrotik goes crazy and
limit stops working (when that happens user have maximum up/down speed of our wimax base station, which
is something we dont like) for this user and this user only for few hours.
User reconnect doesnt help. Mikrotik reboot sometimes help.
Interesting thing is that when this happens, its always related to one user, new users which are connecting
are working properly and they are not affected with this issue.
When this start it ussualy last for few hours and then stops by itself and everything goes back to normal 
We have 2.9.39 version on our locations, but we did 3.26 upgrade on one location hoping this issue will
go away, but it didnt 
Any information regarding resolving this issue is highly appreciated..