Lately hovering does not work well. What can I do?

You may need to do an IMU calibration.

where did you fly your drone? outdoor/indoor?

something in low light situation also cause this by the way try to do an IMU calibration

Sorry to know about your unpleasant experience.   

The hovering status may be affected by the lighting, flight environment,  ground surface etc.  

Try to conduct an IMU calibration first, then fly in the environment full of bright light. ( e. g sunlight) in no wind. Please also be warm reminded that monochrome surfaces ( e.g. pure white ) or highly reflective surfaces would not be suggested.  

Hope this help.