It's gotten a lot better lately but it's still not 100% there yet. Push notifications still aren't reliable, I often find myself getting a notification 10+ minutes after I get a message (sometimes more). It also uses too much mobile data because it seems to be updating too many things on startup.
Do you have discord open on your desktop PC?
10+ minutes sounds like about the amount of time it takes for discord to recognise you're away (ie. auto-away status). If it thinks you're there (ie. online status), then it shouldn't be also pinging your phone. It's the same as when you have discord on your phone and open and it doesn't ping you with every message while you're already looking at it.
I just had a look at Matrix and it seems that the settings let you choose between Off/On/Noisy. Apps like whatsapp default and keep you stuck on "Noisy".
I hope this means that notifications on iOS will actually use the conversations API. As well as making it so that using one of these shortcuts on the app icon no longer takes you to a random message
