This problem is currently occurring in version 7.9.9 of Ignition with Datasets (memory tag) that have a column of type Date (it only happens with the Date type, it does not happen for example with the String type):
First of all you have to create a Dataset with a column of type Date and apply the changes:
Next, one or more rows are added to the Dataset:
It seems that the rows are added without problems, but when applying the changes, the rows and the column of the Dataset are eliminated, and this one takes the value NULL:
I think the problem is related to the date format. Maybe, as I am in Spain there is an internal error of incompatibility.