It’s an in-place upgrade to a new major OS version. It’s nice to see it working out well for users, but nobody can guarantee this.
If it was me, i would (in the following order until something succeeds, hopefully) …
- Turn off the phone (not just a reboot, real shutdown), then turn it on again
- Reseat the SIM card while the phone is turned off (can’t hurt)
- Network reset (search the Settings for “reset” and go with “Reset Wi-Fi, mobile & Bluetooth” or similar)
- Factory reset (search the Settings for “reset”, will delete user data as well as Apps installed by the user and their data)
- OS install from scratch