Update. I figured out the problem. I am with Metro PCS by T-Mobile and my phone switched to 5GUC network and was unable to receive messages. When I went into settings and changed back to LTE phone is working fine now
Had that forever on my last Samsung phone with low cellular strength and dealt with it for years lol. My current Samsung phone has zero issue but it has stronger cellular strength over the last one.
What I used to do is use the carrier app to send and receive messages via wifi. No problem there. You could use it full time as it would just use data when out and about.
Newer phones like yours and mine also include wifi calling (found by swiping down from the top of the screen) so if your carrier offers it and you're on wifi, you can enable wifi calling and set it to preferred. That should be a great way to go if it works well for your situation.
It is also possible to send yourself a message every 10 minutes or whatever and keep it alive but its not a good way to go about it.
If its a different kind of delay then it might be delayed from the carrier. Wifi might still help but if that's delayed then a carrier change should help. Sounds like it wouldn't be this if rebooting the phone helps.
Update. I figured out the problem. I am with Metro PCS by T-Mobile and my phone switched to 5GUC network and was unable to receive messages. When I went into settings and changed back to LTE phone is working fine now
