The new blockchain reactor design specified in #3753 introduces asynchronous message communication between the block processing logic and the request scheduling logic. This async communication introduces latency between the scheduler perceiving bad peer behaviour and informing the processor to remove block provided by that peer. A malicious peer could use this period to saturate the block processing thread and slowing down the FastSync'ing node.

This issue can be solved by yielding the block processing thread to peerErrors at a higher frequency to ensure few if any blocks from an errored peer are processed.