I too am having the same issues. I’m simply not receiving audio text and message notifications. Just the other day I received texts from 4 people in the same short time period; the only notifications I received came from those 2 using Android. But not all Android are getting through, I’m missing audio (and now haptic) notifications from family who use Android. Texts from iOS, have almost now chance of giving me an audio indication, and those from services/ politicians have a very good chance of showing up and interrupting what I’m doing (strangely, not Amazon, though). Location based notifications work great for Target/Walmart/Best Buy with a high level of annoyance if I fail to close those apps.
I thought the problem was with my iPad intercepting messages and texts, but iMessage has been turned off on it for the last month/month and a half.
The only change in my Apple universe was my Apple Watch battery expanded and broke in September, but I was already having issues with random notifications only appearing on the iPad. Everything else is the same (ATT and WiFi).
As for checking DND, I’m not receiving these notifications for my exclusions - those allowed to contact me after hours.
Sorry. I refuse to go “nuclear” on the phone as I had a corrupt backup when wiping/restoring the iPad in October.