My guess is that his client didn't send the reply to any of your read relays.
Hi nostr:npub1syjmjy0dp62dhccq3g97fr87tngvpvzey08llyt6ul58m2zqpzps9wf6wl one thing I don't understand is that I don't see nostr:npub1vg9lk42rxugcdd4n667uy8gmvgfjp530n2307q9s93xuce3r7vzsel8885 replies on my notification window, but all his reactions shows on my notification window. Why reactions works and replies no? Thanks.

Discussion
But why reactions works?
Other thing strange is that some of his reactions shows on notification on PC, but on mobile no. I see many reactions from him on PC, but on mobile only one:

On PC:

It's the opposite of that, haha: https://github.com/CodyTseng/jumble/issues/137
Hum, I closed Jumble on mobile and reopened, and his reactions showed the same as on PC. Maybe is something related to close connection until browser restart?
But his replies notifications, really doesn't show.
nostr:npub1syjmjy0dp62dhccq3g97fr87tngvpvzey08llyt6ul58m2zqpzps9wf6wl
Jumble isn’t optimized for long sessions, so if you keep it open for a long time, there’s no guarantee you won’t miss some events. It could also be a network issue, maybe one of the relays timed out when returning results.
Because his client sent the reactions to your read relays? Haha.
I though that if clients send reactions to my relays, would make sense send the replies too. Crazy thing that no, haha.