I too have being having issues with the Libre app. Well at first I thought it was the Libre app. It has worked pretty much flawlessly for me for just over a year now. I have my alarms set as follows. Low Alarm 5.0, High Alarm 15 and Signal Loss Off. The signal loss alarm was a complete pain. It would wake me 4 or 5 times a night, especially if I was laying on my side and on the sensor.
All worked extremely well, until Samsung updated my S20+ phone just over a month a go. The Libre app started playing up, (no low BG alarm) and constantly showing "Alarms Unavailable". The app that works with my smart watch started playing up, and still is, despite my following the instructions emailed to me to by the manufacturer to resolve the issue. There were settings that used to be available in the menu's that had "disappeared".
Samsung blamed them on the 3rd party apps being at fault, but couldn't answer the question why these apps had suddenly started "playing up" and were working absolutely fine until the latest update they sent for the phone. The phone was running UI4 & Android 12 prior to the update. The latest update has upgraded the phone to UI5 & Android 13.
My sensor is due for replacement tomorrow, and I intend to start the new sensor with an older Samsung S9 phone and see if I can get the alarms to work without any of the current issues I'm experiencing with the Samsung S20+.
The real issue was that I had 2 episodes last week where my BG dropped to around 3 during the night and no alarm to warn me. My saving grace is that I get up every 2-3 hours to go to the bathroom, and I've made it a habit to scan my sensor each time I wake up. So glad I do, because I really felt unwell on both the occasions I reported low BG. Finger pricks done to confirm the low BG were higher than the sensor readings, but enough to alert me that I needed to take action.
I'll you know if going to an older phone resolves the current issues I'm experiencing.