This issue can be reproduced in ZSS Demo.

1. Create a data validation (e.g whole number greater than 0) for a cell.
2. Put an invalid value on the cell (e.g -20)
3. Alert message: invalid data -> OK
4. Instead "try again" or "cancel", close the alert (by clicking X)

After that, user can't change cell's value or even continue to fill the sheet.