Only the Z offset set at "level" can be saved, and the adjusted Z offset value at other times will be lost after the printer is turned off.
If the pom wheel is too tight, it may affect the Z-axis rising, causing the Z-axis to get stuck during the rising process. Thereby affecting the Z offset. If the pom wheel is too tight. You can adjust the eccentric nut at the marked position. Turn it about 1/6 turn each time, and you may need to adjust it multiple times.
The following two items may also affect Z offset; please ignore them if they have already been done.
1. The screws at the marked positions need to be kept loose and cannot be tightened.
2. The X-axis needs to be parallel to the hot bed
https://www.youtube.com/watch?v=SNqO084jRME
3. Turn off the printer power, and then check whether the pins at the marked positions are deformed or damaged.
4. Check whether the proximity swich plug is damaged or loose；You can refer to the video below for the disassembly steps：
*In order to avoid "temperature drift", it is recommended to set the heating bed temperature to 60 degrees Celsius, preheat the heating bed for 10 minutes, and then set the Z offset and level.