I do not think it is a Lidar error , since the reading is quite similar to the barometer altitude reading.
The flare altitude can be set by user LAND_FLARE_ALT or calculated by the autopilot accordingly to the descent rate and altitude with LAND_FLARE_SEC parameter.
You should attach the .bin file of your flight as well as your parameters file so we can check how the LAND and TECS parameters were set.
Basically it does not work , take a look here Arduplane fails calculating descent slope