Sorry for the delay,
We have analyzed the reported query in our end, In our samples we can able to enter a long text in Grid cell and we didn’t able to find any exception. This seems to be any painting / drawing exception. So please provide the below details to us this will help us to provide proper response asap.
1. Let me know the frame work and Syncfusion essential studio version.
2. Please let me know if you have used any drawing method or codes to draw the text in control
3. Please provide any reproducible sample for analysis. This will help us to provide proper solution.