Observable inconsistent state of reactive system is an another pitfall of reactive programming. If the library doesn't provide an way to do an atomic update on several variables at once you end with an sequential updates and each update immediately affect all the system.
Suppose you dealing with bank accounts and each account is represented as a reactive variable, also you have a component which tracks all accounts, aggregate them to a snapshot and send the snapshot to a server. It is natural to think that the sum of money from all account is a const. If your reactive library doesn't provide a way to do atomic updates and you want to do a money transfer via sequential updates you will observe an inconsistent state of snapshot, the sum will fluctuate. If something nasty happens with the network you will have an inconsistent state on the server.