There can be several reasons why your graphs are flat.
The actigraphy is almost flat
When you can see some movement on the actigraphy, but the graph is unusually flat: . Sonar - make sure the signal is strong enough by keeping sonar volume at max at Settings → Sleep tracking → Test sensor → blue sliding bar. - you can also try different frequency by choosing other frequency from the ddrop down menu list in Settings → Sleep tracking → Test sensor → Frequency - keep the phone closer to you bed - try different positioning of the phone . Accelerometer - try keeping the phone closer to you.
This is a companion discussion topic for the original entry at https://docs.sleep.urbandroid.org//faqs/flat_graph.html