datagroup host redirect class match appending original URI

First off, I personally think there are much better and easier ways to do what you are trying to accomplish here since it seems like all you need to do is prepend "; to your requests, but if you are partial to the system you have here, a simple change to your iRule will allow you to keep the URI intact.

when HTTP_REQUEST {
    if { [class match [HTTP::host]/ eq datagrp_redirect] } {
        HTTP::redirect  [class match -value [HTTP::host]/ eq datagrp_redirect ][HTTP::uri]
    }
}

I would highly recommend changing the iRule to be more general such as this:

when HTTP_REQUEST {
    if {[class match [HTTP::host][HTTP::uri] eq datagrp_redirect]}
    {
        HTTP::redirect https://www.[HTTP::host][HTTP::uri]        
    }
}