90% or more deep sleep and no REM at all

I have contacted support already about this. But I thought it might be useful to share it here too.

Suddenly my graphs show that I basically have 90% or more deep sleep and no REM sleep at all. Which doesn’t seem like a healthy sleep pattern.

Saturday 10/19 was the last time the graphs show several REM sleep stages.

I have no clue what changes in my life may have caused this. So just wanted to check if maybe there has been some changes made in the Sleep as Android app.

It seems like the actigraph (the movement intensity graph at the top) is unusually flat. Which sensor do you use?
Could you please send the application log by using Left menu - Report a bug?

My reply:
I use the sonar for sleeptracking. Thanks for your reply. I will send a bug report.

Samsung SM-G960F
Version of Sleep as Android: 20191020

Does this happen on all frequencies?
Vendors tent to enhance the audio experience apply filters to speakers or mic which break sonar. Lately, we have more and more reports solely from Samsung devices, so there was possible some update with a new way of handling the sound stream.

Some phones have troubles with the dynamic one (F18-20), but work well with others. Please, go to Settings -> Sleep tracking -> Test sensor and choose different frequency form the drop down menu list. From our users feedback, seems like the best frequency for Samsung is F18, but this may vary.
And please make sure the sonar volume is at max.

My reply @lenka-urbandroid
I have set the Sonar frequency to F18, as you suggested. It also showed the highest signal strength of all frequencies.
F18: +/- 22000
F19: +/- 16000
F20: +/- 6000
F18-F20: +/- 1800

I’ll let you know if this changed anything.