Problems with bed leveling of Creality CR-10 Mini
The Creality CR-10 Mini is a portal printer using a single Z lead screw at one side of the portal to move the whole X axis gantry. This implies that the X gantry needs to be very stiff when raised and lowered from one side and also have a minimum of play on the rollers (especially on the lead screw driven side). 

I have seen many complaints from experience of people complaining that the gantry is not stiff enough, or that there is too much play on the rollers on either side of the gantry to result in a skew gantry. Consistent leveling is very hard on such machines. A colleague of me added an extra stepper (and split the original stepper connector) to have it raised and lowered from both sides. Do understand that this is also not optimal, missed steps on one of either sides can also cause the X gantry to become skew. A better solution is to create a belt driven extra lead screw that is powered by one stepper, you will not experience a skew gantry as the gantry is integrally moved.