1. Make sure your amplitude and timinng parameters of your circuit meet the LCD spec
2. Make sure your algorithm are matching the spec ie sequence of the command controling LCD, delays and etc.
3. Make sure there is no "noisy" PCB enviroment around LCD interface
4. If you using elastommer connector make sure you have enough pressure
5. Make sure your enviromental conditions match the LCD spec ie temperature huminidity
6. Contact directly to LCD manufactoring to express you concerns and problems
this should be enough for start