no sound or vibration for messages when phone is locked

okay so i have this problem. i have a 17PM, but i have had this exact same problem on past iPhones as well. sometimes (very, very, very frequently) when my phone is locked and i get a text message, it will not make a sound, vibrate or even light up the screen. it'll show on always on display, but the screen won't actually turn on like it does with other notifications. it also affects my apple watch as well (i have the series 10, but ive had this issue with other ones as well). my phone and apple watch are always up to date so i dont know what's causing it. my phone isn't on dnd or any other focus mode, ringer is on, and my watch is always on the charger when its not on my wrist. i know the notifications go to the watch if im wearing it and my phone is locked, but like ive said previously, it does the same thing on my watch as well. on the iphone it sometimes will vibrate and play the notification sound and light up the screen, and sometimes it does none of those. even when my phone is just next to me face up. same for the watch, when wearing it sometimes i get the sound and vibration, and sometimes i get no noitification at all. its really annoying because i miss a lot of messages due to this but idk what to do to fix it. ive looked it up before and tried multiple different fixes but it works when it wants to. i dont have this problem with any other app, only messages