There are three ways to fix it when we are talking about rotary encoder based wheels:
1. First way and the easiest one is to squeeze gently the housing of the encoder with small straight pliers. This increases the pressure between metal teeth and the internal spring which brings better electrical contact
2. Second way is to open it and clean the teeth so they have better contact. After closing the housing it will be also good to squeeze it for better contact
3. Third way and technically harder is to desolder the encoder and change it
