dimpal@08 says:
textmode=date used
TextBox with TextMode Date only supports the yyyy-MM-dd format.
So you need to set the date format before assigning it to TextBox.
The browsers that do not support TextMode Date will show as 2019-08-13, but on browsers that support it will display accordingly.
https://www.aspforums.net/Threads/100041/Set-Date-in-TextBox-when-TextMode-is-Date-using-C-and-VBNet-in-ASPNet/