Hi Mike thanks for posting on the Community!
If you select the column in your Google Sheet that includes the dates and go under Format and select Number > Plain Text your dates will then import accurately if you reinput your data into Smart Containers in Lucidchart. Below is a screenshot of where/how to make this adjustment within Google Sheets.

After you have made that change so the dates are in plain text (rather than Automatic) please reimport your Google Sheet into Smart Containers in your Lucidchart document and they should show up as expected.
Hope this helps!
For anyone else looking for information on importing Google Sheets into Lucidchart please check out our Link Google Sheet Excel or CSV Data to Lucidchart Documents article.