Many people report that ST presence detection has been unreliable on both iOS and Android off and on for many months. Some report that turning off location tracking for a device and then re-enabling it fixes it. Others have given up and moved to other methods for location tracking. Here is a thread about presence detection in 2023
Presence in 2023, including multiple members and multiple locations
You should probably open a ticket with ST Support for them to do a deeper investigation and to add to the growing list of folks who are experiencing this issue.