The issue
Cluey uses your smartphone’s GPS to record your location. In some circumstances, GPS systems may have difficulty obtaining an accurate fix. In such cases, your most recent known position or the location of a nearby mobile phone mast may be recorded instead.
Solutions
Use the Zoom on me function to check on the map whether the GPS fix matches your current location. You may need to repeat this if the GPS does not respond immediately.
Zoom in on the map and long-press the position where you would like to create the Observation.