Geofencing works fine on my S20 as administrator. It shows her location when home. The geofence slider does not do anything. The device shows not present when she is home. Permissions are set the same as my phone. Her Life360 works perfectly. She has a Galaxy S9.
You are not alone here.
I suggest you have a look at the combined presence sensor driver to get better presence readings while combining Life360 or any other presence app with the HE geofence presence.
Update,
I added Life360 to both phones. I appears showing in HE the correct present/not present condition.
My wife's Samsung S9 does not have a geofence circle. The slider does nothing. When tapping the geofence icon, the map starts out in the Atlantic ocean by the equator. When the upper right icon is pressed, it will zoom into the correct location with no geofence circle.
My Samsung S20 map immediately shows my location with the geofence circle that I can change.
Yes, I have installed her Galaxy S9, removed & re-installed it. I tried using both my email address as the admin & her email as the guest. Both phones show in the device list as a virtual & mobile app devices. I have Life360 on both devices.
Does the admin geofence extend to the guest phone? Her phone shows out of geofence.
I reported the same problem with my wife's LG V20 months ago. No geofence at all. You're not the only one with this issue but doesn't seem to be much interest in fixing.