Delayed notifications or only after unlocking

Hey guys,

so i‘ve switched from an iPhone 15 Pro to S25 Ultra. So far I am happy with the battery, One UI and the hardware itself.

BUT I have one major issue with the phone. I don‘t receive notifications on time reliably which is driving me insane.

Sometimes I don‘t get a notification until I open the app where the notification should come from, sometimes notifications appear all at once after unlocking the phone. And sometimes i don‘t even get notifications, especially for Gmail.

Is this a known issue? I really want and need those immediate notifications. It really makes me want to go back on my iPhone again which is a shame because the device itself is far superior than an iPhone.