It’s a standard register form created in a SharePoint WebPart (but this error could happen even if you’re not using SharePoint). When I submit the form, sometimes I loose the information of DropDowns (but not the information of textboxes) and it seems to happen randomly.
I checked the packages sent with Wireshark and I see that the information is sent to the server. I debug the server code and I see that when I try to get the information of DropDowns (to save it to the database) it’s empty.
I load the DropDowns information in the Page_Load event. I used a “if(!Page.IsPostBack)” in order to load the information only when the page is first loaded. The problem is that Page_Load event depends on the network, browser… and this could happen.
Load the DropDown source in the OnInit event. You don’t have to check if it’s postback or not. Directly load the data you need here.