I noticed this after the upgrade too. Sometimes you get only IPv6 connectivity and need to turn off/on mobile data to get IPv4+IPv6 working. Also using Elisa and Xperia10III here.
It’s not a big issue really, push notifications for most messaging apps all work on IPv6 only, and it’s easy to toggle the mobile data when you notice some IPv4 only website not loading.
I also went to purchase a prepaid DNA sim to test out the 5G experience. Download speeds approx 300Mbps on 4G and 150Mbps 400 Mbps on 5G. So some room for improvement on the 5G speeds 
EDIT: Went to a different location to test 5G speeds, and got 400Mbps down instead of 150!