You will prob find that the router is dying because the nat table is filling up, BT will do that, and some of the cheap nasty routers only store state for 127 or 255 connections, and UDP has a ridiculous long timeout on them.

If you are using azureus disable the distributed tracker and distributed DB plugins as those send lots of UDP, and limit your peer connections to 20-30ish and see how it goes.

Otherwise get a real router