Possible reasons:
Electrical:
* Malfunctions of vehicle speed sensors
* Malfunctions in the automatic transmission control unit
*Wiring problems
Mechanical:
* Transmission fluid leaks
* Wear of friction discs
* Torque converter problems
* Oil filter clogged
Software:
* Incorrect settings of the automatic transmission control unit
*Software bugs
Other:
*Weak battery
*Low transmission fluid level
* Contaminated transmission oil
*Excessive engine wear
Solution:
1. Checking the level and condition of the transmission fluid. The level should be normal, and the liquid should be clean, free of foreign particles.
2. Diagnostics of the electronic system. Check the speed sensors, automatic transmission control unit and wiring for faults.
3. Check mechanical components. Repair any fluid leaks, replace worn friction discs, and check the torque converter.
4. Software update. Make sure that the automatic transmission control unit has the latest software.
5. Battery check. A weak battery can cause problems with shifting.
6. Check for other possible causes. Make sure the engine is running properly and there is no excessive wear.
If the problem does not resolve on your own, take it to a qualified mechanic for diagnosis and repair.