Messaging Bug

Ever so often, whilst chatting with a friend, a message I send on my screen wont be received on theirs. I've noticed this a few times while i'm watching their stream that they won't receive it. This also happens vice versa, where they send and i don't receive. It only happens maybe once or twice a few days. There doesn't seem to be any real reason as to why certain messages aren't received, there's no blacklisted words or anything.