Are two major problems.
1) pppoe - so erratic pppoe disconnects all connections simultaneously. (symptom)
2) Interfaces queue - queue type - if you change default ethernet (no single queue of pppoe nor any other to the eye. They should be) to only hardware queue, appear single queue, but not traffic

I am Facing the same problem too, before upgrading to RC14 i didn't have such a problem but unfortunately after RC14 the router started to freez and randomly reboot, then i downgraded to RC13 and the problem continued.

i used to use que trees and PCQ but, the config faild to preform with RC13 and RC14 the ques were saturating, so i switched to Simple ques, but in simple ques from time to another i get wrong bandwidth limiting. which ends up always limiting the user to 2 mbits.