I used to get this on Android 10 too, but not as frequently.
Sometimes notifications only come through when I unlock my device.
It's not a do-not-disturb thing. It's not a "lock screen - hide content/don't show" thing. I do eventually get the notification on the lock screen.
One example is the baby monitor app I use. It doesn't just happen with this, it happens with others, this is just a good example.
If me and the missus are sat watching TV, her phone gets the notification to say motion/sound detected, but mine doesn't.
I can unlock my phone, sometimes a few minutes later, and my phone then vibrates as though the notification _only_ just came through. The time on the notification is the same time that my partner got it, and the time of the motion event, and not the current time.
So it's like the phone queued the notification, or only just retrieved it, once I unlocked my phone.
"Allow background activity" is on, and "Optimise bettery usage" is "Not optimised".
What's going on?
I've been having a seperate issue with mail, as well as the notification issue.
My mail app just stops updating, and I have to force stop (from the app info, not just close it from multi-tasker) before it starts working again.
Unfortunately, some third-party apps may have compatibility issues during Beta 😕. Nonetheless, you can try to report this bug via the Members application, so that our developers can analyze the issue!