After changing motors and putting Lifepo4 battery, vehicle stops intermitently

After motors/gears melted, I bought new motors (aliexpress description says: Children's electric car gearbox with 12V and 6V DC motor,kid's car engine 550 and 390 High speed motor for remote control car), and putting a Lifepo4 battery, everything seems to work, but the vehicle intermitently stops when the load increases. E.g., slight uphill or (moved) grass.

Is this a battery BMS feature, or something with motor, or a controller?

Any easy way to fix it?

Workaround is just to tunr the car off and back on and it works.