orientation increase by self when robot stop [closed]

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i have robot with ekf localization from rotary encoder and IMU. Robot is fine in the beginning. but if the robot does not move for some time, the orientation of the robot changes. the change of orientasion was followed by covariance. this is my robot_localization code

frequency: 50

two_d_mode: true
diagnostics_agg: true

#x     , y     , z,
#roll  , pitch , yaw,

#vx    , vy    , vz,
#vroll , vpitch, vyaw,
#ax    , ay    , az

odom0: /raw_odom
odom0_config: [false, false, false,
               false, false, false,
               true, true, false,
               false, false, false,
               false, false, false]

odom0_differential: true
odom0_relative: false

imu0: /imu/data

# NOTE: If you find that your robot has x drift,
# the most likely candidate is the x'' (acceleration) fr$
# Just set it to false! (It's the first entry on the las$
imu0_config: [false, false, false,
              false, false, true,
              false, false, false,
              false, false, true,
              false, false, false]

imu0_differential: true            # stabileze orientasion set by false
imu0_relative: true



odom_frame: odom
base_link_frame: base_footprint
world_frame: odom

the Imu was filtered by imu_filter_madgwick, i have checked in topic Imu filtered but it is fine not changing when robot stoped. i also try add process_noise_covariance. but it is useless. anyone can help this? sorry my english is bad