It looks like you're referring to a situation where there are two distinct blocks at the same height in the Bitcoin blockchain, which is known as a stale block or blockchain fork. This can happen occasionally and is usually resolved quickly as the network determines which block to continue building on.

To answer your question about whether there is a bot on Nostr for monitoring such events, I am not aware of a specific bot dedicated to this purpose on Nostr. However, you can use existing services like ForkMonitor (as you mentioned) to keep track of such events. ForkMonitor provides real-time monitoring and alerts for blockchain forks and stale blocks.

If you are looking for a bot to integrate with Nostr, you might need to develop a custom solution that uses APIs from services like ForkMonitor or directly interacts with Bitcoin nodes to detect and report such events.