*Redirect http to https for Internet clients but not private clients*

Maybe try adding the following logging entries to the HTTP_REQUEST section of your iRule to ensure that your source IP and redirect variable values are what you expect....

log local0. "Client IP = [IP::client_addr]\n";
log local0. "redirect variable equals $redirect\n";

Then from the cli do a "tail -f /var/log/ltm" to see the values.

I concur. You can also save yourself the trouble of a variable assignment by putting everything in one event:

when HTTP_REQUEST {
    log local0. "incoming IP: [IP::client_addr]"
    if { ( [IP::addr [IP::client_addr] equals 10.0.0.0/8] ) or ( [IP::addr [IP::client_addr] equals 192.168.1.0/24] ) } {
        log local0. "local address - allowing"
        return
    } else {
        log local0. "remote address - redirecting"
        HTTP::redirect "https://[HTTP::host][HTTP::uri]"
    }
}