Alerts & Notifications not apparent when Phone Unlocked & In Use

Hey there. I have noticed in the last few months for the first time that I am not getting notifications and alerts when actively using the phone.
Previously if I set an alarm or received a text while flicking around facebook as an example, I would at least get a split second vibration or noise or a screen pop up asking me to stop the alarm so I knew something was happening. I am now finding that alarms or timers I set aren't going off at all and that I have new text messages that came in while I was in an app that was not accompanied with a vibration or alert of any kind. I have not changed any settings at all. I am using an SE and have the last IOS update.
I can only assume the phone thinks that because the screen is unlocked and in use that the more apparent alerts aren't necessary. I can appreciate that for a sighted person but it's really messing with me. Especially when timing cooking and awaiting communication.
Thoughts?