@Ramr-msft Thanks for the reply!
I also noticed that in one-to-one chats this delay happens but the application manages to send notification messages. On the contrary, it occurs with a group that has, for example, 20 people.
I've already waited for up to 24 hours to see if he could send it but he still couldn't, could this indicate something about my problem? Any configuration I should do in the bot?