I noticed on the 10 ii with SFOS 4.1.0.24 that every now and then the screen lights up, but when I take a look at it, I cannot see any notification. So no new mail, no telegram message etc.
Also no system notification can be seen (e.g. storeman updates available).
Why does the screen light up?
Same behaviour here. In my case, the reason are muted Whatsapp groups. Messages to that groups don’t create notifications, but cause the display to light up.
Cannot be the reason for me since I don’t have whatsapp installed. But maybe its muted telegram groups 
Or it is a side effect of silent SMS from your local secret service? 
I noticed the same on my XA2. The only silent group is in Threema.
Don’t know what you mean with local secret service, but as of today I haven’t installed any SIM card.
I had the same problem already with SFOS 4.0 on my XA2. I have some silent telegram groups. With SFOS 4.1 I didn’t noticed this behaviour yet. But I use it just for 2 days…
Are you using any Android Apps? Some of those are using notifications to prevent the Android system from putting them to sleep. One of the Android apps I’m usually using (Conversations) is creating a notification every minute, causing the screen to light up (though it is showing a notification).
If so, you can adjust the notifications in the android settings of the app and disable notifications for those “keep alive” ones.