I have 2 related issues with my Note 20 Ultra.
1. I live in a low signal area. My phone will often roam to another network when at home. When I go back into town the phone is often very slow to return to the home network.
2. When my phone does go back to its home network, it is more often than not on 3G mode only, and doesn't switch to LTE. I have to toggle flight mode on then off again and it will switch to LTE.